Resistance of Tuta absoluta to insecticides Because

Transcrição

Resistance of Tuta absoluta to insecticides
Because of the short generation time and the frequent applications of insecticide to manage T. absoluta
resistance to several insecticides has developed.
In 1999 significant resistance of T. absoluta to acephate and deltamethrin was reported1. In the same
year resistance to deltamethrin, lamba=cyhalothrin, mevinphos, metamidophos and esphenvalerate was
reported in Chile2.
In 2000 resistance to Cartap was reported in Brazil3,4. In 2001 resistance to abamectin was additionally
reported in Brazil4,5. In 2005 an Argentine study confirmed T. absoluta resistance in that country to
deltamethrin and abamectin as well as methamidophos6.
Among the widely used insecticides that are still effective are imidacloprid7 and Bacillus thruingiensis.
References
1.
CASTELO BRANCO, M.; FRANÇA, F.H., MEDEIROS, M.A.; LEAL, J.G.T. Uso de inseticidas para o controle da
traça-do-tomateiro e traça-dascrucíferas: um estudo de caso. Horticultura Brasileira, v. 19 n. 1, p. 60-63, março, 2001.
2.
SALAZAR E.; ARAYA J. Tomato moth, Tuta absoluta (Meyrick) response to insecticides in Arica, Chile.
Agric. Téc. v.61 n.4 Chillán oct. 2001
3.
SIQUEIRA H. A. A. ,GUEDES R. N. C.; PICANCO M. C. Cartap resistance and synergism in populations of Tuta
absoluta (Lep., Gelechiidae). J. Appl. Ent. 124, 233-238. 2000
4.
SIQUEIRA H. A. A. ,GUEDES R. N. C.; PICANCO M. C . Insecticide resistance in populations of Tuta
absoluta (Lepidoptera: Gelechiidae). Agricultural and Forest Entomology. Volume 2, Issue 2, Pages 147-153. 2001
5.
SIQUEIRA H. A. A., GUEDES R. N. C, FRAGOSO D. B and MAGALHA L. C. Abamectin resistance and synergism
in Brazilian populations of Tuta absoluta (Meyrick) (Lepidoptera: Gelechiidae) International Journal of Pest Management.
47(4) 247-251. 2001
6.
LIETTII M., BOTTOII E., ALZOGARAY R. Insecticide resistance in Argentine populations of Tuta absoluta (Meyrick)
(Lepidoptera: Gelechiidae). Neotrop. Entomol. vol.34 no.1 Londrina Jan./Feb. 2005
7.
DANTE.M; GIMÉNEZ R. Efficacy of imidacloprid to control the tomato borer (Tuta absoluta meyrick).
IDESIA (Chile) V 26, Nº 1, p 65-67. 2008
CASTELO BRANCO, M.; FRANÇA, F.H., MEDEIROS, M.A.; LEAL, J.G.T. Uso de inseticidas para o controle da traça-do-tomateiro e traça-dascrucíferas: um estudo de caso. Horticultura Brasileira, v. 19 n. 1, p. 60-63, março, 2.001.
Uso de inseticidas para o controle da traça-do-tomateiro e traça-dascrucíferas: um estudo de caso.
Marina Castelo Branco1; Félix H. França1; Maria A. Medeiros1, José Guilherme T. Leal2
Embrapa Hortaliças, C. Postal 218, 70.359-970, Brasília - D.F; E-mail: [email protected] 2/EMATER-DF. Escritório Local
Núcleo Rural da Taquara, s/n. 70.000-000 Brasília – DF
1/
RESUMO
ABSTRACT
Em agosto de 1999, produtores de tomate e brassicas da Núcleo
Rural da Taquara tiveram seus cultivos seriamente comprometidos
devido à impossibilidade de controle da traça-do-tomateiro e da traça-das-crucíferas. Diversos inseticidas, alguns com o mesmo princípio ativo ou, pertencentes ao mesmo grupo químico, eram aplicados de uma a sete vezes por semana sem qualquer eficiência no
controle das pragas. Lavouras foram abandonadas em diferentes estádios
de desenvolvimento. A fim de definir uma estratégia de controle
que viabilizasse a produção de tomate e brassicas na região, foi avaliado em laboratório a eficiência da dose comercial de alguns inseticidas usados no controle das duas pragas. Para isso, foram coletadas
duas populações de traça-do-tomateiro e uma população de traçadas-crucíferas. Para traça-do-tomateiro, cartap, abamectin, lufenuron,
acefate e deltametrina causaram respectivamente 100; 90; 67 e 0%
de mortalidade das larvas. Para traça-das-crucíferas, B. thuringiensis,
abamectin, cartap, acefate and deltametrina causaram 100; 96; 86;
79 e 5% de mortalidade respectivamente. De acordo com estes resultados foi recomendada a suspensão imediata do uso de piretróides
e organofosforados para o controle das duas pragas. Abamectin e
cartap foram recomendados para o controle da traça-do-tomateiro e
B. thuringiensis para o controle de traça-das-crucíferas.
Use of insecticides for controlling the South American Tomato
Pinworm and the Diamondback Moth: a case study.
Palavras-chave: Brassica oleracea, Lycopersicon esculentum,
Tuta absoluta, Plutella xylostella, tomate, repolho, couve-flor,
controle químico, resistência a inseticida.
Keywords: Brassica oleracea, Lycopersicon esculentum, Tuta
absoluta, Plutella xylostella, tomato, cabbage, cauliflower,
chemical control, insecticide resistance.
In August 1999, at the “Núcleo Rural da Taquara”, Federal
District, Brazil, tomato and brassica crops were severely damaged
by the South American Tomato Pinworm (Tuta absoluta) and the
Diamondback Moth (Plutella xylostella). During that time growers
related that they had been spraying insecticides one to seven times
per week without controlling the pests. In the fields it was observed
that there were crops with different ages and levels of chemical
residues which allowed the pests to multiplicate continuously. Then
it was decided that the first step to solve the problem would be to
evaluate the efficacy of the recommended field rate of some
insecticides in laboratory bioassays. Two Brazilian Tomato Pinworm
populations and one Diamondback Moth population were collected.
Cartap, abamectin, lufenuron, acephate and deltamethrin caused 100;
90; 67 and 0% of larval mortality to the South American Tomato
Pinworm, respectively. B. thuringiensis, abamectin, cartap, acephate
and deltamethrin caused 100; 96; 86; 79 and 5% of mortality to the
Diamondback Moth, respectively. According to laboratory results it
was recommended that the use of pyrethroid and organophosphorous
compounds must be suspended immediately. Abamectin and cartap
must be used to control the South American Tomato Pinworm and
B. thuringiensis must be employed to Diamondback Moth control.
(Aceito para publicação em 04 de janeiro de 2.001).
E
m agosto de 1999, foi verificado que
no Núcleo Rural da Taquara (DF) a
produção de tomate e brassicas estava
seriamente comprometida devido aos
danos ocasionados pela traça-do-tomateiro (Tuta absoluta) e pela traça-dascrucíferas (Plutella xylostella). Diversos tipos de inseticidas, com freqüência
que variava de semanal a diária, foram
utilizados na região. A impossibilidade
de controle das pragas foi atribuída, pelos agricultores, à possível “falsificação
dos produtos”. Não foi levantada a hipótese de que a ineficiência dos produtos poderia ser devida à resistência das
pragas aos inseticidas. Resistência de
traça-do-tomateiro a cartap já foi observada no Brasil (Siqueira et al., 2.000) e
60
resistência de traça-das-crucíferas a diversos inseticidas já foi observada em
várias partes do mundo (Castelo Branco
& Gatehouse, 1997; Cameron & Walker,
1998; Baker, 1999; Kovaliski, 1999).
Observações preliminares de tomate
do local constataram a presença de minas de traça-do-tomateiro em praticamente todas as folhas e, em alguns casos, até 100% de frutos danificados. Em
lavouras de brassicas foram observados
furos de traça-das-crucíferas em folhas
de repolho e couve-flor e, em um cultivo
de couve-flor, foram encontradas mais de
100 larvas/planta. O sistema de produção destas culturas envolvia: plantio contínuo e sucessivo de tomate e brassicas;
abandono de restos culturais nas áreas de
cultivo; mistura de inseticidas; utilização
em rotação de dois ou três produtos diferentes, em uma mesma semana, sem observação de critérios técnicos.
Zhao et al. (1995), em ensaios realizados na China, observaram que testes
de laboratório onde se avaliava a eficiência da dose comercial de inseticidas para
o controle da traça-das-crucíferas eram
bons indicadores da eficiência dos inseticidas em campo. A fim de determinar
quais os inseticidas ineficientes para o
controle da traça-das-crucíferas e traçado-tomateiro no Núcleo Rural da
Taquara, testes de laboratório foram realizados. De posse destes dados e das observações de campo, recomendações para
o manejo da cultura foram sugeridas.
Hortic. bras., v. 19, n. 1, mar. 2001.
Uso de inseticidas para o controle da traça-do-tomateiro e traça-das-crucíferas: um estudo de caso.
MATERIAIS E MÉTODOS
1. Populações coletadas
Foram coletados ovos, larvas e
pupas de duas populações de traça-dotomateiro (Populações 1 e 2) e de uma
população de traça-das-crucíferas (População 3) no Núcleo Rural da Taquara.
Os agricultores forneceram dados sobre
os inseticidas utilizados e freqüência de
aplicação, conforme segue:
1.1 Traça-do-tomateiro: abamectin,
Bacillus thuringiensis, chlorfluzuron,
ciflutrina, deltametrina, fenpropatrina,
lufenuron, metomil, permetrina e
triflumuron. As pulverizações foram
realizadas com um inseticida ou com
mistura de produtos a cada 24 horas.
1.2 Traça-do-tomateiro: abamectin,
Bacillus thuringiensis, betaciflutrina,
ciflutrina, cartap, fenpropatrina,
lufenuron, metomil, permetrina,
triflumuron. As pulverizações eram realizadas a cada três dias, com um inseticida ou com mistura de dois inseticidas
(piretróide + lufenuron).
1.3 Traça-das-crucíferas: abamectin,
chlorfluzuron, deltametrina, metamidofós
e outros inseticidas não identificados. As
pulverizações eram feitas com intervalo que variavam de um a três dias.
2. Bioensaios
2.1. Traça-do-tomateiro: Foram
utilizadas larvas de segundo e terceiro
estádio de traça-do-tomateiro provenientes diretamente do campo. Os inseticidas abamectin (9 g.i.a./ha), acefate (750
g.i.a./ha), cartap (625 g.i.a./ha),
deltametrina (10 g.i.a./ha) e lufenuron
(40 g.i.a./ha) foram diluídos considerando-se o volume de calda de 1.000 L/ha.
Folíolos que não continham larvas de
traça-do-tomateiro foram imersos na
solução de inseticida por 10 segundos
e, em seguida, colocados para secar a
temperatura ambiente. Após estarem
secos, 10-15 larvas de traça-do-tomateiro foram colocadas em três folíolos em
placa de Petri (15 cm de diâmetro). Em
outro teste, folíolos infestados com larvas de traça-do-tomateiro foram imersos
na solução de inseticida por 10 segundos (10-15 larvas/repetição) e transferidos para placas de Petri. Foram utilizadas quatro repetições por tratamento.
Para todos os inseticidas, a mortalidade de larvas foi avaliada após 24 h,
exceto para lufenuron, onde a mortalidade de larvas foi avaliada após seis
dias. Para este último inseticida foi ainda avaliado o número de adultos emergidos. Para a população 1 foram testados abamectin, acefate, deltametrina e
lufenuron. Para a população 2 foram testados acefate, cartap e deltametrina. Os
produtos cuja mortalidade de larvas foi
superior a 90% foram considerados como
eficientes para o controle da praga.
Para a análise estatística foi utilizado o esquema fatorial 5 x 2 e 4 x 2 [inseticidas x posição das larvas nas folhas
(sobre ou dentro das minas)] para as
populações 1 e 2, respectivamente. Os
dados foram submetidos à análise de
variância e ao teste DMS (p<0,05) para
a separação das médias.
2.2.Traça-das-crucíferas: Larvas e
pupas foram coletadas em cultivo de
couve-flor e criadas em laboratório até
a emergência de adultos. Os adultos foram liberados em gaiola contendo folhas de repolho para a obtenção dos ovos
os quais foram mantidos em caixas plásticas com folhas de repolho até que as
larvas se desenvolvessem até o segundo estádio, quando foram utilizadas no
bioensaio. Foi avaliada a eficiência dos
seguintes inseticidas: acefate (750 g i.a./
ha), abamectin (9 g i.a./ha), Bacillus
thuringiensis (18 g i.a./ha), cartap (300
g i.a./ha) e deltametrina (6 gi.a./ha). As
diluições foram realizadas considerando-se um volume de calda de 400 l/ha.
Discos de folhas de repolho de 4 cm
de diâmetro foram imersos na solução
inseticida e secos à temperatura ambiente, no laboratório. Foram transferidos
para placas de Petri com 9 cm de diâmetro e sobre cada folha foram colocadas 15 larvas de traça-das-crucíferas.
A mortalidade de larvas foi avaliada após 48 h. Os dados foram submetidas à análise de variância e foi utilizado
o teste DMS (p<0,05) para a separação
de médias.
2.3. Inimigos naturais: Um total de
50 ovos de traça-do-tomateiro foram
coletados no campo em cada uma das
duas áreas de tomate. Os ovos foram
individualizados em cápsulas de gelatina para a verificação de ocorrência de
parasitóides.
Larvas de traça-das-crucíferas
coletadas no campo foram também separadas e criadas até o estágio de pupa.
Quando as pupas foram obtidas (172 no
total), foram individualizadas em cápsulas de gelatina para a observação da
emergência de parasitóides ou adultos
da praga.
RESULTADOS E DISCUSSÃO
1. Traça-do-tomateiro: Para as duas
populações de traça-do-tomateiro houve apenas efeito do inseticida na mortalidade das larvas. Não houve efeito da
posição das larvas sobre os folíolos (larvas sobre os folíolos ou no interior destes) nem da interação inseticida x posição das larvas. Este resultado é diferente do observado por Castelo Branco &
França (1993) onde, quando folhas de
tomate foram tratadas com cartap, a
mortalidade de larvas de traça-do-tomateiro no interior das minas foi significativamente menor do que a mortalidade
de larvas sobre as folhas. A causa desta
diferença não pôde ser identificada, mas
é possível que o grau de suscetibilidade
das populações ao inseticida de alguma
maneira interfira nos resultados.
As doses comerciais dos inseticidas
deltametrina e acefate causaram a mortalidade de menos de 2% das larvas das
populações 1 e 2 (Tabelas 1 e 2).
Lufenuron ficou em uma posição
intermediária, causando entre 67 e 72%
de mortalidade das lagartas (Tabela 1).
No entanto, este produto, por ser um
regulador de crescimento, afeta também
a emergência de adultos. Uma média de
13% dos adultos emergiram, quando as
larvas foram colocadas sobre as folhas.
Já quando as larvas estavam dentro das
folhas, este percentual subiu para 26%.
Ainda que mais de 10% dos adultos da
traça-do-tomateiro tenham emergido,
inseticidas reguladores de crescimento
como lufenuron afetam a fertilidade de
fêmeas (França & Castelo Branco,
1996), podendo contribuir para a redução da população da praga em campo.
Abamectin causou a mortalidade de
mais de 90% das larvas da população 1
(Tabela 1) e cartap causou a mortalidade de todas as larvas da população 2
(Tabela 2). Estes resultados indicam que
estes dois inseticidas são os produtos
61
M. Castelo Branco et al.
Tabela 1. Mortalidade de larvas de traça-do-tomateiro tratadas com diferentes inseticidas. Larvas sobre folhas ou no interior das minas.
População 1. Taquara, Embrapa Hortaliças, 1999.
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número de larvas encontradas após 24 h para todos os inseticidas a exceção de Match®, onde o número de larvas é o número de larvas
encontrado após seis dias.
Médias seguidas de mesma letra não diferem entre si pelo teste DMS (p> 0,05)
1/
Tabela 2: Mortalidade de larvas de traça-do-tomateiro tratadas com diferentes inseticidas. Larvas sobre folhas ou no interior das minas.
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número de larvas encontradas após 24 h para todos os inseticidas a exceção de Match®, onde o número de larvas é o número de larvas
encontrado após seis dias.
1/
mais eficientes para o controle da praga
na região.
Dos 50 ovos da traça-do-tomateiro
coletados de cada população, nenhum
parasitóide emergiu. Este resultado pode
indicar a ausência de parasitóides na
região ou a eliminação destes.
2.
Traça-das-crucíferas:
Deltametrina foi o produto menos eficiente, causando a mortalidade de menos de
6% das larvas (Tabela 3). Acefate e
cartap se situaram em uma posição intermediária com uma mortalidade variando de 79 a 86% (Tabela 3).Abamectin e
Bacillus thuringiensis causaram morta62
lidade superior a 96% (Tabela 3). Estes
resultados indicaram uma boa eficácia
dos dois inseticidas para o controle da
praga. Abamectin não é registratdo para
a cultura de brássicas, não tendo portanto o seu uso recomendado.
Das 172 pupas de traça-dascrucíferas obtidas, apenas duas estavam
parasitadas. Uma por Apanteles sp. e a
outra por Oomyzus sokolowiskii. Entre
as pupas 87 originaram adultos e 83 não
emergiram. Esta baixa ocorrência de
parasitóides pode ser atribuída ao elevado número de aplicações de inseticida e ao uso de produtos extremamente
tóxicos como por exemplo metamidofós
e deltametrina (Talekar & Yang, 1991;
Kao & Tzeng, 1992). Este resultado difere do observado por França &
Medeiros (1998) onde em uma avaliação de inseticidas em campo foi observada população alta de parasitóides (média > 4,0 adultos por planta) nas parcelas tratadas com deltametrina, indicando a sobrevivência destes no local do
experimento. Como nesta área de cultivo foram utilizados diferentes tipos de
inseticida, não foi possível a identificação dos produtos que mais contribuíram
para a redução da população dos
Uso de inseticidas para o controle da traça-do-tomateiro e traça-das-crucíferas: um estudo de caso.
parasitóides. Estudos que visem avaliar
a seletividade de alguns destes produtos se fazem necessários.
É sabido que as doses recomendadas de qualquer inseticida são capazes
de matar um determinado percentual da
população da praga, geralmente 95%,
independentemente da sua densidade
populacional (Knipling, 1979). Então,
quando a densidade populacional é baixa, os produtos tendem a ser mais eficientes do que quando a densidade
populacional é mais elevada. No Núcleo
Rural da Taquara, o sistema de produção de tomate e brassicas (plantios sucessivos e não eliminação de restos culturais) e as condições ambientais (tempo
quente e seco) eram favoráveis ao crescimento descontrolado das populações de
traça-das-crucíferas e traça-do-tomateiro (França et al., 1985; Haji et al., 1988;
Castelo Branco, 1992). Deste modo, nenhum inseticida, mesmo os considerados
eficientes em testes de laboratório, apresentaram eficiência no campo.
Assim, para a viabilização de lavouras de tomate e brassicas na região e
sobrevivência de parasitóides e predadores que possam auxiliar na redução
das populações das pragas, são necessárias a implementação de medidas racionais de uso de inseticidas e outras
práticas de manejo da cultura que visem,
principalmente, reduzir as condições
favoráveis ao crescimento populacional
dos insetos. São recomendadas as seguintes medidas:
a) pulverizações semanais de inseticidas;
b) eliminação de inseticidas pertencentes a grupos químicos considerados
ineficientes nos testes de laboratório;
c) introdução de um esquema de rotação de inseticidas (Castelo Branco, 2.000);
c) uso de irrigação por aspersão para
remoção de ovos e mortalidade de larvas e pupas (Costa et al., 1998;
Junqueira et al., 1998);
d) destruição de restos culturais;
e) não utilização de plantio
seqüenciado de tomate ou brássicas.
As recomendações aqui descritas
foram seguidas por um agricultor do
Núcleo Rural da Taquara e com isso foi
recuperada uma lavoura de tomate e um
plantio de couve-flor que já haviam sido
considerados perdidos.
Tabela 3 Mortalidade de larvas de traça-das-crucíferas tratadas com diferentes inseticidas.
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AGRADECIMENTOS
A Hozanan P. Chaves pelo auxílio
nos trabalhos de campo e laboratório.
Aos agricultores do Núcleo Rural da
Taquara pelas informações prestadas.
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63
Agricultura Técnica
Agric. Téc. v.61 n.4 Chillán oct. 2001
RESPUESTA DE LA POLILLA DEL TOMATE, Tuta absoluta
(Meyrick),
A INSECTICIDAS EN ARICA1
Tomato moth, Tuta absoluta (Meyrick) response to
insecticides in Arica, Chile
Erika R. Salazar2 y Jaime E. Araya3
1
Recepción de originales: 22 de noviembre de 1999.
Instituto de Investigaciones Agropecuarias, Centro Regional de Investigación La
Platina, Casilla 439, Correo 3, Santiago, Chile.
3
Universidad de Chile, Facultad de Ciencias Agronómicas, Departamento de Sanidad
Vegetal, Casilla 1004, Santiago, Chile. E-mail: [email protected]
2
ABSTRACT
Larval susceptibility of Tuta absoluta (Meyrick) collected on tomato (Lycopersicon
esculentun Mill.) crops in Azapa, Arica (18º 31 S lat, 70º 11 W long), Chile, was
compared by toxicological tests with several commonly used insecticide doses applied
on two development stage larvae groups (stadia 1-2 and 3-4). To determine resistance
to insecticides, LD50, LD90, and regression slopes between probit mortality and log
dosage were calculated. Resistance to studied insecticides was verified, since LD50 at
least doubled those in Ovalle and Quillota, locations where T. absoluta had the
greatest resistance in other study. Deltamethrin and mevinphos were the least and
most toxic compounds, respectively. Larvae of both development levels were equally
susceptible to deltamethrin, while larger larvae were more resistant to mevinphos than
smaller ones. Results with esfenvalerate and O - cyhalothrin on large larvae, and
metamidophos on small larvae, were too variable and this caused a defective probit
analysis and resistance evaluation to these insecticides in such larval groups. Parasite
may have also developed resistance to insecticides; this may explain the resurgence of
populations in the Valley. Possible parasite resistance, which are present even with
insecticide treatments at extremely high dosages, could have affected accuracy in the
regressions obtained, particularly on large larvae.
Key words: Deltamethrin, esfenvalerate, O - cyhalothrin, mevinphos, metamidophos.
RESUMEN
Se comparó la susceptibilidad larvaria de la polilla del tomate, Tuta absoluta
(Meyrick), colectada en tomate (Lycopersicon esculentun Mill.) en Azapa, Arica (18º
31 lat. Sur, 70º 11 long. Oeste), mediante pruebas de toxicología con varias dosis de
insecticidas de uso común, aplicados sobre grupos de larvas de dos niveles de
desarrollo (estadíos 1-2 y 3-4). Para determinar la resistencia a los insecticidas se
calcularon las DL50, DL90 y pendientes de las regresiones entre mortalidad (probit) y
dosis (log). Se verificó la resistencia a los insecticidas estudiados, pues las DL50 al
menos duplicaron aquellas en Ovalle y Quillota, localidades donde T. absoluta
presentó la mayor resistencia en otro estudio. Deltametrina y mevinfos fueron los
compuestos menos y más tóxicos, respectivamente. Las larvas de ambos niveles de
desarrollo fueron igualmente susceptibles a deltametrina, mientras que las larvas
grandes fueron más resistentes a mevinfos que las pequeñas. Los resultados con
esfenvalerato y O - cihalotrina sobre larvas grandes, y metamidofos en larvas
pequeñas fueron muy variables, lo que impidió un buen ajuste probit y la evaluación
de resistencia a estos compuestos en dichos grupos larvarios. El parásito también
puede haber desarrollado resistencia a insecticidas, lo que puede explicar que en el
Valle se hayan restablecido sus poblaciones. La posible resistencia de parásitos,
presentes incluso en tratamientos insecticidas a dosis extremadamente altas, podría
haber afectado la precisión de las regresiones obtenidas, especialmente sobre larvas
grandes.
Palabras clave: Deltametrina, esfenvalerato, O - cihalotrina, mevinfos, metamidofos.
INTRODUCCIÓN
La polilla Tuta absoluta (=Scrobipalpuloides absoluta) (Meyrick) (Lepidoptera:
Gelechiidae) es clave en el cultivo del tomate (Lycopersicon esculentum Mill.) en
Chile (González, 1989; Prado, 1991); en cada temporada, el cultivo requiere
aplicaciones frecuentes de insecticidas para evitar una reducción drástica de la
producción y calidad de los frutos (Vargas, 1970; Apablaza, 1984). Salazar y Araya
(1997) describieron la importancia de los daños y comprobaron el desarrollo de
resistencia a algunos de estos compuestos mencionado por diversos autores (Acuña,
1970; Vargas, 1970; Campos, 1976; Moore, 1983) en varias localidades productoras.
Los insecticidas pueden aumentar los rendimientos al reducir los daños causados por
las plagas, pero su uso repetido puede seleccionar gradualmente insectos resistentes
(Lockwood et al., 1984; Brattsten, 1989; Metcalf, 1989).
Los cultivos de tomate en el Valle de Azapa reciben 15-17 aplicaciones de numerosos
insecticidas en la temporada para controlar a T. absoluta, muchas veces en mezclas y
con dosis mayores a las comerciales, lo que sugiere el desarrollo de resistencia. El
objetivo de este estudio fue evaluar en laboratorio, con una metodología simple y de
bajo costo, la efectividad de algunos insecticidas de uso habitual en el control de la
polilla del tomate en el Valle de Azapa, utilizando larvas obtenidas en rastrojos de
tomate.
MATERIALES Y MÉTODOS
Las pruebas se hicieron con larvas colectadas en rastrojos de tomate en el Valle de
Azapa, en el Centro de Investigación y Capacitación Agrícola (CICA), San Miguel de
Azapa (18º 31 lat Sur; 70º 11 long Oeste), Universidad de Tarapacá (a 12 km de
Arica), en 1995. Se evaluaron los piretroides deltametrina (Decis 2,5 EC®),
esfenvalerato (Halmark 7% LE®) y O - cihalotrina (Karate 5% EC®), y los fosforados
mevinfos (Phosdrin 24% LE®) y metamidofos [Monitor 600 (g L-1) CS®], por su
amplia utilización por productores de tomate (Salazar y Araya, 1997).
Las larvas se colectaron del follaje de rastrojos de tomate con pincel y se utilizaron
diariamente, manteniendo el excedente a baja temperatura (alrededor de 5ºC) para uso
en pruebas posteriores. En cada tratamiento se usaron larvas pequeñas (estadíos 1-2,
de 1,0-2,5 mm de longitud) y grandes (estadíos 3-4, de 4,5-7,5 mm). Las larvas de
2,5-4,5 mm se descartaron, para separar claramente ambos tamaños larvarios.
En las pruebas se determinó la mortalidad por contacto, asperjando con un aspersor
manual De Vilbiss 1 mL de solución insecticida sobre grupos de 20 larvas
seleccionadas al azar, en placas Petri inclinadas 45° de la horizontal, con papel filtro
N°1 en el fondo. Aspersiones sobre papel fotográfico determinaron una gota similar a
la de la torre Potter utilizada por Salazar y Araya (1997) y el aspersor manual a 1 m
entre el aspersor y la placa Petri en este estudio. Se aplicaron al menos cinco dosis
crecientes por insecticida y tamaño larvario, desde las dosis mínimas comerciales (0,4
mL L-1 de mezcla insecticida para los piretroides, y 1 ó 2 mL L-1 para los fosforados
metamidofos y mevinfos, respectivamente), con tres repeticiones por tratamiento. Una
vez secas, las larvas tratadas se trasladaron a frascos con follaje fresco de tomate sin
insecticida y se mantuvieron a 18±2°C. La mortalidad se evaluó a las 48 h,
considerando muertas aquellas larvas sin motilidad al ser estimuladas con pincel.
Para verificar la acción de cada insecticida (Busvine, 1980), los resultados de
mortalidad se corrigieron por la fórmula de Abbott (1925) y procesaron mediante
análisis probit (Finney, 1971; Busvine, 1980), siguiendo la metodología aplicada por
Salazar y Araya (1997), para calcular, utilizando el programa computacional POLO
PC, las DL50, DL90 y pendientes de las regresiones entre mortalidad (probit) y dosis
(log). Se realizaron pruebas de Chi2 para comprobar el ajuste entre las mortalidades
obtenidas y las esperadas, y corroborar el análisis probit. Las DL50 se analizaron
mediante análisis de varianza; los promedios se separaron mediante pruebas de rango
múltiple de Duncan (1955). Las diferencias estadísticas entre las pendientes de las
regresiones se evaluaron mediante la prueba t de Student.
RESULTADOS Y DISCUSIÓN
Los resultados del análisis por insecticida se presentan en los Cuadros 1-3. Al no
obtenerse mortalidad mayor al 90% con dosis razonables de insecticida, algunos DL90
se estimaron con las ecuaciones obtenidas con el programa POLO PC.
El Cuadro 1 presenta las DL50, intervalos de confianza al 95% y pendientes ±
desviación estándar de la regresión lineal de los insecticidas evaluados.
Cuadro 1. Respuesta de larvas de Tuta. absoluta de San Miguel de Azapa, Arica1.
Table 1. Tuta absoluta larvae response from San Miguel de Azapa, Arica1.
Insecticidas
DL50
Intervalo
de Pendiente ± desviación estándar
confianza al 95%
Estadíos 1-2
Deltametrina
571,26
201,30 - 412,09
2,72±0,31
Esfenvalerato
46,12
_
1,18±0,25
O - cihalotrina
35,28
17,40 - 332,94
0,96±0,16
Mevinfos
21,45
-
3,11±0,42
Estadíos 3-4
Deltametrina
476,09
_
2,39±0,46
Mevinfos
35,84
26,02 - 53,76
23,29±0,35
Metamidofos
24,21
_
1,94±0,29
1
Las poblaciones no presentaron distribución normal, lo que impidió su análisis estadístico.
Las pruebas de Chi2 indicaron que las rectas log (dosis) x mortalidad de esfenvalerato
y O - cihalotrina para larvas grandes (estadíos 1-2), y metamidofos para larvas
pequeñas (estadíos 3-4), no se ajustaron a poblaciones de distribución normal de
tolerancia, lo que impidió su análisis estadístico. Sin embargo, a pesar que la
metodología en este ensayo es menos precisa que la que utiliza la torre Potter,
igualmente se constató la poca eficiencia y la posible resistencia a los insecticidas
estudiados, pues las DL50 obtenidas al menos duplican aquellas determinadas para
Ovalle y Quillota, localidades con los mayores niveles de resistencia en el estudio de
Salazar y Araya (1997).
Deltametrina no causó diferencias significativas de susceptibilidad entre ambos
tamaños larvarios, aunque la mayor DL50 numérica ocurrió con las larvas pequeñas
(Cuadro 2). Este resultado, diferente a los obtenidos por Salazar y Araya (1997) en
otras localidades, pudo deberse al diferente método de aplicación de los insecticidas.
En el tratamiento con mevinfos las larvas grandes fueron más resistentes que las
pequeñas.
Cuadro 2. DL50 (mL L-1) de los dos grupos larvarios (estadios 1-2 y 3-4) de Tuta
absoluta de San Miguel de Azapa, Arica, tratados con cinco insecticidas1.
Table 2. LD50 (mL L-1) of both larval groups (stadia 1-2 and 3-4) of Tuta absoluta
from San Miguel de Azapa, Arica, treated with five insecticides1.
Larvas
Estadíos 1-2
Estadíos 3-4
Deltametrina 571,26 a
447,09 a
Esfenvalerato 46,12
-
O
35,27
cihalotrina
-
Mevinfos
35,84 a
21,45 b
Metamidofos 1
24,21
Promedios en cada columna con letras iguales no son diferentes significativamente (P=0,05).
El signo - indica que no hubo un buen ajuste probit.
Para las larvas de San Miguel de Azapa, deltametrina y mevinfos fueron los
compuestos de menor y mayor toxicidad, respectivamente (Cuadro 3).
Cuadro 3. Resistencia relativa de las larvas de Tuta absoluta de San Miguel de
Azapa, Arica, a los insecticidas, en DL50 múltiplos de la dosis comercial1.
Table 3. Tuta absoluta larvae from San Miguel de Azapa, Arica, relative resistance to
the insecticides, in LD50-folds of the commercial dosage1.
Ingrediente activo
Estadíos 1-2
Estadíos 3-4
Deltametrina
1428,16 a
1117,72a
Esfenvalerato
115,30 b
-
O - cihalotrina
88,19 b
-
Mevinfos
17,92 c
10,72 c
Metamidofos
-
24,21 b
1
Promedios en cada columna con letras iguales no son diferentes significativamente (P=0,05).
El
signo
indica
que
no
hubo
un
buen
ajuste
probit.
Salazar y Araya (1997) encontraron factores de resistencia (FR) a deltametrina de 7,1
y 8,2 para larvas grandes y pequeñas, respectivamente, de T. absoluta de Ovalle, y
además confirmaron la resistencia a este piretroide en Quillota y Colina. También
encontraron resistencia a esfenvalerato en Ovalle y Quillota, e incipiente en Colina,
con FR de 2,0 y 1,9 para larvas grandes y pequeñas, respectivamente. Las mayores
DL50 para O - cihalotrina en larvas pequeñas y grandes ocurrieron en Ovalle y
Quillota, respectivamente, con un menor nivel de resistencia en Colina. Sin embargo,
estos autores indicaron que podrían haber subestimado los FR para deltametrina y
esfenvalerato, debido a las altas dosis requeridas en ambos casos para matar al 50%
de la población (control) susceptible de Requinoa, la que ya tendría algún grado de
resistencia a estos insecticidas. Las poblaciones de Ovalle, Quillota y Colina fueron
menos susceptibles a O - cihalotrina. Las de Ovalle, Quillota y Colina fueron menos
susceptibles para metamidofos que las de Requinoa. Para mevinfos, los mayores FR
ocurrieron en Ovalle (5,45 y 4,72 para larvas grandes y pequeñas, respectivamente).
Para todas las localidades, mevinfos fue el insecticida de mayor toxicidad relativa y
por ende más efectivo. Sin embargo, el uso de este insecticida fue prohibido en Chile
en
1995
por
el
Servicio
Agrícola
y
Ganadero.
En todas las localidades evaluadas por Salazar y Araya (1997), las larvas 3-4 fueron
menos susceptibles a los insecticidas estudiados, en general con DL50 1,2-2,5 veces
mayores que para larvas de menor desarrollo (estadíos 1-2). Estos resultados
confirman otros informados en la literatura, pues la susceptibilidad a un producto
químico disminuye con el aumento del tamaño larvario (Busvine, 1980).
En la comparación de Salazar y Araya (1997) de la toxicidad relativa de los
insecticidas evaluados, mevinfos y deltametrina fueron los compuestos más y menos
tóxicos, respectivamente, sobre todas las poblaciones de T. absoluta. De los
piretroides evaluados para todas las localidades y tamaños larvarios, O - cihalotrina
fue el más tóxico. En Ovalle, mevinfos y O - cihalotrina fueron el fosforado y el
piretroide más tóxicos. Metamidofos fue más tóxico que O - cihalotrina sobre larvas
grandes, mientras que ambos insecticidas no se diferenciaron estadísticamente en
larvas pequeñas. En Quillota, mevinfos y O - cihalotrina fueron los insecticidas más
tóxicos. Los fosforados fueron más tóxicos que los piretroides en larvas grandes,
mientras que mevinfos fue más tóxico que O - cihalotrina sobre larvas pequeñas.
Metamidofos fue el tercer insecticida en toxicidad. En Colina, mevinfos y O cihalotrina fueron también los insecticidas más tóxicos; se observó además, un
aumento en la toxicidad de esfenvalerato sobre los resultados para Quillota y Ovalle,
aunque sin diferencia estadística con metamidofos. En Requinoa, al igual que en las
otras localidades, mevinfos y O - cihalotrina fueron los compuestos más tóxicos.
Ambos insecticidas presentaron resultados similares, con DL50 cercanos a las dosis
comerciales recomendadas. Destacaron además, las DL50 para deltametrina sobre los
estadíos 3-4 (29,85 veces) y 1-2 (12,34 veces), lo que evidenció una alta resistencia
para deltametrina en esta localidad.
Si los resultados se comparan con los de Salazar y Araya (1997), se puede concluir
que la población de Azapa ha desarrollado alta resistencia a los insecticidas
estudiados. Esta hipótesis debe ser comprobada, sin embargo, utilizando una
metodología de precisión similar a la de ese estudio, e incluyendo una población
control susceptible.
Durante la evaluación de mortalidad se observaron algunas larvas grandes con alguna
motilidad al estimulo con pincel, pero con tegumento marrón oscuro, por lo que se
consideraron muertas. En otros recuentos se encontraron pupas de parásitos adosadas
al cuerpo de las larvas de T. absoluta, revelando que aquellas larvas oscuras
consideradas muertas estaban parasitadas. Se criaron algunas pupas, las que sin
embargo se deshidrataron y no produjeron parasitoides adultos para su identificación.
El parásito también puede haber desarrollado resistencia a insecticidas, lo que ha
permitido que en el Valle de Azapa se restablezcan sus poblaciones (Vargas, 1970).
La posible resistencia de parásitos larvarios es lógica al encontrarse larvas y/o pupas
en sectores tratados con insecticidas en concentraciones extremadamente altas. Este
factor podría haber afectado la precisión de las regresiones en los tratamientos sobre
larvas grandes.
Una forma razonable de manejar la resistencia a los plaguicidas son programas de
manejo integrado que reduzcan la frecuencia e intensidad de la selección y apliquen
un mejor control natural y cultural, y el uso de variedades resistentes. En conjunto,
estas medidas pueden eliminar gran parte de los individuos seleccionados antes que
produzcan una progenie resistente a insecticidas (Metcalf, 1980). Para el manejo
integrado es vital disminuir la presión de selección, aplicar insecticidas con menor
frecuencia, evitar el uso de compuestos persistentes en el ambiente, formulaciones de
lenta liberación, compuestos con presión de selección en varios estados de desarrollo
del insecto, e incorporar métodos alternativos biológicos y culturales (Metcalf, 1980,
1989). Para manejar los insecticidas se deben analizar las poblaciones para conocer la
susceptibilidad original y detectar temprano el desarrollo de resistencia, de manera de
extender la vida útil de un insecticida hasta que la respuesta de la población indique la
necesidad de cambiarlo. La secuencia de insecticidas alternativos debe limitar los
compuestos con resistencia simple y cruzada (e.g., dimetoato y piretroides) y el uso de
mezclas insecticidas. Se debe considerar el umbral económico, utilizar métodos
adecuados y aplicación oportuna, usar plaguicidas inocuos para los enemigos
naturales, y productos selectivos en vez de compuestos tóxicos de amplio espectro.
Aunque la metodología en este trabajo logró resultados muy variables y fue menos
precisa que la utilizada por Salazar y Araya (1997) con una torre Potter en laboratorio,
nuestros resultados comprobaron la ineficacia de los insecticidas más utilizados contra
T. absoluta en el Valle de Azapa, verificando el deterioro ambiental y productivo
causado por la intervención con insecticidas de amplio espectro en ambientes poco
diversificados y ecológicamente inestables. Se debe estudiar la incorporación de
nuevos compuestos insecticidas con diversos modos de acción, de manera de evitar el
desarrollo de resistencia y/o regenerar el sistema productivo de tomates en el extremo
norte de Chile, con el objeto de proteger esta importante actividad agrícola, fuente de
ingresos para numerosos productores durante todo el año, y evitar repetir situaciones
de crisis productivas de tipo regional como las descritas por Metcalf (1989).
CONCLUSIONES
Aunque la metodología utilizada permitió una medición rápida de la pérdida de
efectividad de los insecticidas más utilizados contra la polilla del tomate en el Valle
de Azapa, algunos resultados fueron muy variables, lo que impidió un buen ajuste
probit y la evaluación consiguiente de resistencia a estos compuestos. Estos estudios
pueden afinarse mediante el uso de una torre de precisión tipo Potter y la comparación
con una población susceptible. También se debe estudiar el desarrollo de resistencia a
insecticidas en los enemigos naturales de T. absoluta, con miras a su posible
utilización en programas de control integrado de esta plaga.
AGRADECIMIENTOS
Los autores agradecen la valiosa colaboración del Ingeniero Agrónomo Sr. Juan
Machuca del Servicio Agrícola y Ganadero, Arica, y de los entomólogos Sres. Héctor
Vargas y Dante Bobadilla, CICA, San Miguel de Azapa, Universidad de Tarapacá.
LITERATURA CITADA
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Econ. Entomol. 18:265-267.
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(Meyr.). IDESIA, Universidad del Norte (Chile) 1:75-110.
[ Links ]
Apablaza, J. 1984. Incidencia de insectos y moluscos plagas en siete hortalizas
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Publication Titles
Agricultural and Forest Entomology
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Volume 2, Issue 2, Pages 147-153
Published Online: 24 Dec 2001
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Insecticide resistance in populations of Tuta absoluta (Lepidoptera: Gelechiidae)
Herbert Álvaro A. Siqueira, Raul Narciso C. Guedes and Marcelo C. Picanço
Departamento de Biologia Animal, Universidade Federal de Viçosa, Viçosa, MG 36571 000, Brazil
Correspondence: Raul Narciso C. Guedes. Tel: + 55 31 899 2006; fax: + 55 31 899 2537; e-mail: [email protected]
KEYWORDS
Abamectin • cartap • methamidophos • permethrin • tomato leafminer
ABSTRACT
Abstract
1 Control failures of insecticides used against the tomato leafminer Tuta absoluta (Meyrick) (Lepidoptera: Gelechiidae) in Brazil
led to the investigation of the possible occurrence of resistance of this insect pest to abamectin, cartap, methamidophos and
permethrin.
2 The insect populations were collected from seven sites in the states of Minas Gerais, Rio de Janeiro, and São Paulo. These
populations were subjected to concentration–mortality bioassays using insecticide-impregnated filter papers.
3 We were unable to obtain a single population which provided a susceptibility standard for all insecticides tested. Therefore,
the resistance levels were estimated in relation to the most susceptible population to each insecticide. Resistance to abamectin
and cartap were observed in all populations when compared with the susceptible standard population, with resistance ratios
ranging from 5.2- to 9.4-fold and from 2.2- to 21.9-fold for abamectin and cartap, respectively. Resistance to permethrin was
observed in five populations with resistance ratios ranging from 1.9- to 6.6-fold, whereas resistance to methamidophos was
observed in four populations with resistance ratios ranging from 2.6- to 4.2-fold.
4 The long period and high frequency of use of these insecticides against this insect pest suggest that the evolution of
insecticide resistance on them has been relatively slow. Alternatively, the phenomenon might be widespread among Brazilian
populations of T. absoluta making the finding of suitable standard susceptible populations difficult and leading to an
underestimation of the insecticide resistance levels in this pest.
5 Higher levels of resistance to abamectin, cartap and permethrin are correlated with greater use of these compounds by
growers. This finding suggests that local variation in insecticide use was an important cause of variation in susceptibility.
Accepted: 14 April 2000;
DIGITAL OBJECT IDENTIFIER (DOI)
10.1046/j.1461-9563.2000.00062.x About DOI
Introduction
The tomato leafminer Tuta absoluta (Meyrick) (Lepidoptera: Gelechiidae) is an oligophagous insect which attacks solanaceous
crops, especially tomato, where it is one of its main pests ( Picanço et al. 1998 ). This insect was originally described in Peru,
but it is widespread throughout South America ( Povolny 1975; Carballo et al. 1981 ; Muszinski et al. 1982 ; Souza & Reis
1 de 7
1/11/2010 2:48 PM
M
1986). It was initially reported in Brazil between September 1979 and October 1980 at Morretes county, state of Paraná, from
where it spread throughout the country, and has been considered a serious problem for tomato production since then (
Muszinski et al. 1982 ; Souza & Reis 1986; França 1993; Guedes et al. 1994 ; Picanço et al. 1995 ).
The larval injury to the tomato plant leads to direct yield loss. The leafminers attack the tomato plants in all of their
developmental stages, damaging the stems, apices, flowers and fruits besides mining their leaves ( Souza et al. 1992 ; Miranda
et al. 1998 ). This kind of damage resembles those of other Gelechiidae pests of solanaceous crops, such as Keiferia
lycopersicella (Wals.) in Central and North America and Phthorimaea operculella (Zell.) in the Americas, Europe, Africa and
Asia ( Sannino & Nicodemo 1979; Juvick et al. 1982 ; Abbas et al. 1993 ; Ebora et al. 1994 ; Pouey et al. 1994 ). When in high
densities, T. absoluta is able to cause significant production losses in tomato crops ( Souza et al. 1992 ; Picanço et al. 1998 ).
The main control method for T. absoluta is the use of insecticides, but some of the compounds recommended for its control are
apparently not providing the desired effect ( Castelo Branco & França 1992; Guedes et al. 1994 ). It has been hypothesized that
excessive insecticide applications commonly applied to the tomato crop during a single cultivation period, sometimes up to 36
sprays, could have led to the evolution of resistant populations, besides eliminating their natural enemies, and leading to
additional occupational hazards ( Castelo Branco & França 1992; Gonçalves et al. 1994 ; Picanço et al. 1995 ).
Permethrin and cartap were initially the only insecticides for use against T. absoluta, leading to their large scale utilization in
Brazil for a long period ( Souza & Reis 1986). The use of abamectin and methamidophos is more recent (i.e. early 1990s) and
abamectin, in mixture with mineral oil, shows high efficiency against the pest ( Guedes et al. 1995 ; Castelo Branco et al. 1996 ;
Picanço et al. 1998 ). However, some investigators pointed out that the use of mineral oil in insecticide mixtures can increase
problems of insecticide resistance in insect pest populations ( Castelo Branco et al. 1996 ; Picanço et al. 1996 ).
Insecticide resistance has been reported all over the world to almost every group of insecticides used against insect pests (
Lockwood et al. 1984 ; Georghiou 1986; Kay & Collins 1987). Therefore, it is necessary to develop management tactics to delay
or even prevent the evolution of insecticide resistance in insect pest populations, and the detection and monitoring of such
phenomena is of key importance to achieve this ( Dennehy et al. 1983 ; Tabashnik & Roush 1990). Owing to control failures of
insecticides used against T. absoluta and the report of resistant populations of this pest in Chile ( Moore 1983; Salazar & Araya
1997), the present study was carried out to detect the existence of Brazilian populations of T. absoluta resistant to the main
insecticides used against it and to quantify that resistance and its relationship with insecticide use in seven sites in Brazil.
Materials and methods
Five populations of T. absoluta from the state of Minas Gerais, one population from the state of Rio de Janeiro, and another
from São Paulo ( Fig. 1; Table 1) were used in this study. These last two populations were obtained from laboratory colonies,
established from local populations, with intended use as potential standard susceptible populations. For each of these sites,
information on insecticide use was obtained from appropriate growers or State extension personnel. Colonies of T. absoluta
were established from at least 200 larvae obtained from heavily infested leaves from each sampling site. The individual
populations were reared on tomato plants of variety Santa Clara, without insecticide exposure, enclosed in cages and
maintained in a greenhouse.
Fig. 1 Sites of origin of the populations of tomato leafminer (T.
absoluta) in the Brazilian states of Minas Gerais, Rio de Janeiro and
São Paulo. The numbers correspond to locations indicated in
Table 1.
[Normal View ]
Table 1 Origin and year of collection of populations of the tomato leafminer (T. absoluta).
Code number
County
State
Place
1
2
3
4
5
6
7
Araguari
Guiricema
Lavras
Uberlândia
Viçosa
São João da Barra
Paulínia
Minas Gerais
Field
Minas Gerais
Field
Minas Gerais
Field
Minas Gerais
Field
Minas Gerais
Field
Rio de Janeiro Laboratory
São Paulo
Laboratory
Month and year collected
August 1998
September 1998
August 1998
April 1998
October 1997
August 1997
August 1998
The four technical grade insecticides used were abamectin (Novartis Biociências, São Paulo, SP), cartap (Iharabrás, Sorocaba,
SP), methamidophos (Bayer, São Paulo, SP), and permethrin (Zeneca Agrícola, Holambra, SP). All of these insecticides are
currently recommended for controlling T. absoluta in Brazil.
Insecticide bioassays were carried out using insecticide-impregnated filter paper (9 cm diameter) placed in Petri dishes (9 cm
diameter × 1.5 cm height). For each bioassay, six to seven different insecticide concentrations were applied; control treatments
(acetone for abamectin and permethrin, ethanol for methamidophos, and distilled water for cartap) were included. Three
replicates with 20 second instar larvae of T. absoluta were used at each insecticide concentration. For each replicate, we used
a filter paper impregnated with 1 mL of insecticide dissolved in the appropriate solvent (i.e. acetone, ethanol or distilled water).
Insecticide concentrations were calculated as µg a.i./cm2 of treated surface. Insects were counted as dead if they were unable
to walk. Concentration–mortality data were subjected to probit analysis (Proc Probit, Sas Institute 1997).
Correlation analysis (Proc CORR, Sas Institute 1997) was used to test the association between the insecticide use and its
resistance ratio across the sites studied. No association between insecticide use and resistance ratio could result from poor
estimation of insecticide use, resistance ratio, or both, or lack of a causal relationship between insecticide use and resistance
ratio. In addition, multiple regression analysis (Proc REG, Sas Institute 1997) was used to determine whether the use of the
other insecticides contributed to variation in resistance ratio of a particular insecticide. The dependent variable (i.e. the
resistance ratio of a particular insecticide) was used in the multiple regression models to test the four independent variables (i.e.
the use of each of the four insecticides under investigation).
Results
The results of Ȥ2 test (Ȥ2 and P values) used to measure how well the data of each concentration–response curve fit the
assumptions of the probit model are presented on Tables 2–5. As values (responses) predicted by the probit model did not differ
2
significantly from values actually observed in the bioassays (low Ȥ -values and P > 0.05), the probit model was suitable for the
concentration–response analyses.
Table 2 Comparative susceptibility of populations of tomato leafminer (T. absoluta) to permethrin.
LC50 (95% CL)
Population
n
Slope ± SEM µg a.i./cm
Uberlândia
Viçosa
Paulínia
Lavras
São João da Barra
Araguari
Guiricema
421
362
360
422
360
420
365
0.51 ± 0.04
0.63 ± 0.07
0.70 ± 0.07
0.56 ± 0.09
0.58 ± 0.08
0.80 ± 0.07
0.86 ± 0.07
2
47.8 (39.2–59.0)
71.5 (58.7–85.9)
89.3 (76.6–103)
142 (108–219)
158 (117–290)
187 (165–212)
316 (273–361)
LC90 (95% CL)
µg a.i./cm 2
Resistance
ratio *
Ȥ2
Prob.
319 (221–532)
389 (275–669)
305 (237–447)
575 (325–2194)
528 (289–4475)
600 (469–875)
1088 (845–1628)
–
1.50
1.87
2.97
3.31
3.90
6.61
4.06
6.37
0.26
9.57
7.80
5.63
2.59
0.54
0.17
0.99
0.09
0.10
0.34
0.63
* LC 50 resistant/LC50 susceptible.
Table 3 Comparative susceptibility of populations of tomato leafminer (T. absoluta) to abamectin.
LC50 (95% CL)
Population
n
Uberlândia
Paulínia
Guiricema
São João da Barra
Viçosa
Lavras
Araguari
360 0.80 ± 0.10
361 0.76 ± 0.12
360 0.67 ± 0.06
420 0.45 ± 0.03
421 0.49 ± 0.04
360 0.67 ± 0.08
360 0.63 ± 0.09
2
LC90 (95% CL)
µg a.i./cm 2
0.97 (0.87–1.09)
2.40 (1.99–3.14)
5.00 (4.21–5.81)
18.2 (14.5–25.1)
5.87 (4.90–6.96)
21.9 (16.8–32.3)
5.96 (4.51–7.52)
48.7 (35.1–76.7)
6.76 (5.28–8.37)
47.1 (34.8–71.2)
8.31 (7.10–9.87)
34.7 (25.1–56.6)
9.09 (7.68–10.92) 36.0 (25.3–65.0)
Resistance
ratio *
Ȥ
–
5.16
6.04
6.14
6.97
8.57
9.37
4.34
3.30
2.80
1.19
1.93
0.48
6.79
2
Prob.
0.36
0.51
0.59
0.95
0.86
0.98
0.15
Table 4 Comparative susceptibility of populations of tomato leafminer (T. absoluta) to methamidophos.
LC50 (95% CL)
Population
n
São João da Barra 362 0.67 ± 0.06
Viçosa
401 0.62 ± 0.07
Lavras
420 0.67 ± 0.05
Uberlândia
440 0.80 ± 0.11
Araguari
343 2.17 ± 0.42
Paulínia
400 1.16 ± 0.17
Guiricema
400 1.23 ± 0.16
2
LC90 (95% CL)
µg a.i./cm 2
59.9 (50.9–70.8) 243 (184–357)
62.3 (53.9–72.1) 192 (154–256)
79.3 (53.4–99.0) 239.6 (204–305)
155 (137–175)
530 (420–744)
191 (179–201)
279 (263–303)
225 (202–246)
473 (421–556)
252 (228–275)
535 (473–637)
Resistance
ratio *
Ȥ2
–
1.04
1.32
2.59
3.19
3.76
4.22
7.75 0.10
8.06 0.15
7.78 0.17
8.10 0.23
5.34 0.25
5.66 0.34
7.51 0.19
Prob.
Table 5 Comparative susceptibility of populations of tomato leafminer (T. absoluta) to cartap.
LC50 (95% CL)
Population
n
Paulínia
Guiricema
Lavras
Uberlândia
Viçosa
São João da Barra
Araguari
363 1.90 ± 0.21
363 2.24 ± 0.52
420 1.90 ± 0.20
400 1.04 ± 0.13
420 0.71 ± 0.10
420 0.77 ± 0.04
341 1.01 ± 0.11
2
LC90 (95% CL)
µg a.i./cm 2
Resistance
ratio *
0.44 (0.41–0.47)
0.74 (0.67–0.84) –
0.97 (0.92–1.03)
1.60 (1.39–2.19) 2.25
1.87 (1.76–1.98)
3.15 (2.89–3.55) 4.22
4.57 (4.13–5.04)
10.4 (9.08–12.5) 10.4
4.81 (4.22–5.47)
15.5 (12.5–20.7) 10.9
7.16 (6.34–8.18)
20.9 (16.8–28.1) 16.2
9.68 (8.47–10.87) 25.3 (21.3–32.4) 21.9
Ȥ
2
5.34
4.68
5.06
4.30
5.44
6.66
6.86
Prob.
0.25
0.32
0.41
0.51
0.36
0.25
0.14
There was significant variation in the susceptibility among the insect populations studied for the four insecticides investigated
based on the criterion of failure of 95% CL at the LC50s to overlap. We were unable to identify a general standard susceptible
population. Therefore, the resistance ratios were taken by comparison with the population most susceptible to each insecticide.
The population from Uberlândia was the most susceptible one for permethrin and abamectin ( Tables 2 and 3), whereas São
João da Barra was the most susceptible to methamidophos ( Table 4) and Paulínia was most susceptible to cartap ( Table 5).
LC50s for permethrin were significantly greater for five of the populations of T. absoluta relative to the population from
Uberlândia ( Table 2). LC50 for the population from Viçosa resembled that of Uberlândia and Paulínia, differing from the
remaining ones. Permethrin resistance ratios ranged from 1.5- to 6.6-fold among the populations of the leafminer studied. LC50s
for abamectin were significantly greater for all insect populations when compared with the population from Uberlândia, with
resistance ratios ranging from 5.2- to 9.4-fold ( Table 3).
Resistance to methamidophos was observed in only four insect populations when compared with the population from São João
da Barra, the most susceptible one to this insecticide ( Table 4). These four populations were from Araguari, Guiricema,
Paulínia and Uberlândia, and their resistance ratios to methamidophos ranged from 2.6- to 4.2-fold. By contrast, the populations
from Lavras and Viçosa were susceptible to this insecticide. Resistance to cartap was observed in all of the populations studied
in comparison with the most susceptible one ( Table 5), as was observed for abamectin, but with a different susceptibility
standard. The cartap resistance ratios ranged from 2.3- to 21.9-fold among the T. absoluta populations.
Slopes of the concentration–mortality curves for permethrin and abamectin were relatively similar among the different insect
populations. However, there was a greater variation in slopes for the insecticides methamidophos and cartap, with some
populations showing slopes twice as great as those of some others. These high slopes of concentration–mortality curves
probably reflect a higher homogeneity of response to these insecticides in these populations ( Finney 1971).
Insecticide use varied among sites and the total number of sprays per cultivation cycle per site ranged from seven to 22, the
number of applications in Uberlândia and Araguari, respectively. Overall number of sprays per cultivation cycle per site for
abamectin (mean = 4.3, range = 0–8) and cartap (mean = 4.7, range = 0–8) were greater than for methamidophos (mean = 3.0,
range = 0–10) and permethrin (mean = 1.4, range = 0–3). Variation in use of each insecticide was significantly correlated with
the variation in resistance ratio for the same insecticide ( Fig. 2), except for methamidophos (r= í 0.36, P= 0.42). Multiple
regression analyses showed that the use of other insecticides did not contribute to the resistance ratio of any particular
insecticide. Only the use of the insecticide to which the resistance has been observed provided good regression models, with
the exception of methamidophos, for which we were unable to obtain any significant model (dferror = 5, F= 9.88, P= 0.02 and
2
2
r = 0.66 for abamectin resistance; dferror = 5, F= 17.08, P= 0.01 and r = 0.77 for cartap resistance; dferror = 5, F= 4.23, P=
2
2
0.10 and r = 0.46 for methamidophos resistance; dferror = 5, F= 9.13, P= 0.03 and r = 0.65 for permethrin resistance).
Fig. 2 Correlations between number of sprays per cultivation cycle and
resistance ratio of T. absoluta for the same insecticide across seven
sites.
[Normal View ]
Discussion
Among the insecticides investigated here, only resistance to methamidophos had been previously recorded in Chilean
populations of T. absoluta ( Salazar & Araya 1997). Resistance of T. absoluta to abamectin, cartap and permethrin is reported
here for the first time. The resistance levels observed in Brazilian populations of the tomato leafminer are relatively low
(< 10-fold), but they are possible causes of the control failures with these insecticides ( Souza et al. 1992 ).
There were significant differences in the resistance levels among different populations for each insecticide. Such variability in
resistance levels indicates the occurrence of differential selection pressures, genetic diversity in the resistance mechanisms
among the insect populations, or both ( Kerns & Gaylor 1992). The response to abamectin was similar among the resistant
insect populations, but there was greater variability of response among populations for the other insecticides. This may be
caused by the different level of use of these compounds in the different areas from where the populations were obtained. The
resistance levels were lower for permethrin and methamidophos, and greater for abamectin and cartap, which may be due to a
higher selection pressure provided by the more intensive use of abamectin and cartap ( Souza et al. 1992 ; Picanço et al. 1995
), or the lack of good susceptible standard populations, especially for the insecticides methamidophos and permethrin,
underestimating the resistance to these two compounds.
The persistence of an insecticide on a plant leads to the continuous selection of resistant individuals, which may contribute to a
faster resistance evolution ( Roush 1989). The lower resistance levels to permethrin in comparison with cartap, compounds
used for about the same length of time in Brazil, might be due to the lower persistence of the former, leading to a lower selection
pressure for resistance on the leafminer populations ( Souza & Reis 1986; Guedes et al. 1994 ). In addition, permethrin is
mainly used during the tomato harvest, due to its short pre-harvest interval, unlike cartap, which may have favoured a stronger
selection pressure for cartap resistance ( Guedes et al. 1994 ). Despite the low permethrin resistance levels in Brazilian
populations of T. absoluta observed in our study, the more resistant populations of this insect were obtained from areas of high
frequency of insecticide application and where there were reports of chemical control failures, as in the counties of Araguari and
Guiricema ( Souza et al. 1992 ; Picanço et al. 1995 ).
The populations of T. absoluta showed low levels of resistance to methamidophos, similar to those observed for permethrin.
This may be due to the relatively lower efficiency of this compound in controlling T. absoluta compared to abamectin and cartap,
for example, as reported by Souza et al. 1992 ) . This is probably one of the reasons for its lesser use in comparison with the
other compounds, as well as its high toxicity to mammals ( Ware 1994). The resistance levels to methamidophos reported here
for Brazilian populations of T. absoluta resemble those for Chilean populations ( Salazar & Araya 1997).
Abamectin resistance has never been reported in T. absoluta before, despite suspicions of the occurrence of this phenomenon
in different populations of this pest as a result of its widespread use, usually in mixture with mineral oil ( Guedes et al. 1995 ;
Castelo Branco et al. 1996 ; Castelo Branco et al. 1996 ). The use of mineral oil in mixture with abamectin apparently increases
the persistence of the insecticidal effects on the plant ,exerting a higher selection pressure on the pest population ( Castelo
Branco et al. 1996 ). The use of the insecticide alone does not seem to produce strong selection pressure for resistance
because of the low doses used in the field and its fast degradation in the environment without bioaccumulation ( Clark et al.
1994 ). The low levels of resistance to abamectin observed in our study suggest that the importance of mineral oil in the
evolution of abamectin resistance in T. absoluta is probably overestimated. The low variability in response to this insecticide
among different populations of the pest insect is probably a reflection of its widespread use throughout Brazil.
Cartap resistance has not been the object of much attention. The only studies on the subject are those reported by Liu et al.
(1982) and Cheng 1988) with the diamondback moth Plutella xylostella. Our results indicate resistance to cartap in Brazilian
populations of T. absoluta. The observed cartap resistance levels in T. absoluta reached moderate levels (> 10-fold and <
100-fold) in four of the populations studied (i.e. Uberlândia, Viçosa, São João da Barra and Araguari), with the highest level
observed in the population from Araguari (22-fold). Such resistance levels are a probable explanation for the control failures with
cartap against T. absoluta reported by França 1993) . However, Castelo Branco et al. 1996 ) suggested that the low efficiency
of cartap against T. absoluta was probably due to a poor application technology. However, our results do not provide support
for this contention. Nevertheless, poor application may be a contributing factor to the low efficiency of cartap in controlling
resistant populations of T. absoluta in some areas. The low to moderate levels of resistance to cartap and the long period of
use of this insecticide in Brazil suggest that the resistance to cartap has a slow rate of evolution in populations of T. absoluta.
The significant positive correlations between frequency of application and resistance ratio suggest that the variation in
susceptibility of T. absoluta populations was caused by local variation in insecticide use. The only exception to this observation
was the insecticide methamidophos, whose resistance ratios were not significantly correlated with its use, probably due to a
poor estimation of this insecticide use in São João da Barra, where it is commonly used (10 sprays per cultivation cycle). The
population collected in this site was the most susceptible to this insecticide. After eliminating these data from the correlation
analysis (for methamidophos), there was a significant and positive correlation between frequency of methamidophos application
and its resistance ratio across the remaining sites (r= 0.88, P= 0.02). The results obtained with the multiple regression did not
suggest any pattern of cross-resistance among the insecticides studied.
In summary, our data indicate that populations of T. absoluta from Brazil show resistance to abamectin, cartap, methamidophos
and permethrin, confirming the suspicions raised by other investigators (e.g. Souza et al. 1992 ; França 1993; Guedes et al.
1994 ). The resistance levels ranged from low (< 10-fold) to moderate (> 10-fold and < 100-fold) levels for the main insecticides
used for a long time, which suggests a low rate of evolution of this phenomenon in T. absoluta, but also explains some of the
control failures observed with the use of these compounds against this insect. Alternatively, the phenomenon might be
widespread among Brazilian populations of T. absoluta, making finding suitable standard susceptible populations difficult and
leading to an underestimation of the insecticide resistance levels in this insect. This is one of the few reported cases of
resistance to cartap in insect pests reaching moderate levels in some populations. This finding opposes claims of poor
application technology as the sole explanation of control failures with the use of this insecticide against T. absoluta. The
correlations between insecticide use and resistance ratio across seven sites suggest that local variation in insecticide use was
an important cause of variation in susceptibility. There was no evidence of cross-selection among the insecticides studied.
Acknowledgements
We would like to express our gratitude to Nilton C. Picinato (DuPont) and Norma E. Pereira (Universidade Estadual do Norte
Fluminense) for providing the T. absoluta populations from Paulínia (SP) and São João da Barra (RJ), respectively; and to the
agrochemical companies Iharabrás, Novartis Biociências, Zeneca Agrícola and Bayer for providing the technical grade
insecticides used in this study. The information about insecticide use provided by growers and State extension personnel was
greatly appreciated. We also would like to thank A. D. Watt and three anonymous referees for their valuable suggestions.
Financial support was provided by FAPEMIG, CNPq and CAPES and is acknowledged here.
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Accepted 14 April 2000
INTERNATIONAL JOURNAL OF PEST MANAGEMENT, 2001, 47(4) 247±251
Abamectin resistance and synergism in Brazilian populations of Tuta absoluta (Meyrick)
(Lepidoptera: Gelechiidae)
(Keywords: tomato leafminer, Brazil, insecticide resistance, diethyl maleate, piperonyl butoxide, triphenylphosphate)
H. A. A. SIQUEIRA, R. N. C. GUEDES*, D. B. FRAGOSO and L. C. MAGALHAÄES
Departamento de Biologia Animal, Universidade F ederal de VicË osa, VicË osa, MG 36571-000, Brazil
Abstract. Failures in the control of the tomato leafminer Tuta absoluta
(Meyrick) by means of abamectin in Brazil, and a recent report of
abamectin resistance in Brazilian populations of this pest species, led to
the investigation of the possible involvement of detoxification enzymes
using insecticide synergists. Resistance to abamectin was observed in
all populations when compared with the standard susceptible population, with resistance ratios ranging from 5.2- to 9.4-fold. Piperonyl
butoxide was the most efficient synergist with abamectin synergism
ratios ranging from 3.0- to 5.3-fold and providing significant resistance
suppression, but complete suppression of abamectin resistance was
only obtained in one population of T. absoluta. Triphenylphosphate was
an abamectin synergist which was not as efficient as piperonyl butoxide,
but it provided complete suppression of abamectin resistance in four of
the six resistant populations studied, suggesting a major involvement of
esterases as an abamectin resistance mechanism in these populations.
The importance of cytochrome P450, inhibited by piperonyl butoxide,
seems secondary to esterases. Diethyl maleate also synergized
abamectin in nearly all populations, but provided only partial suppression of abamectin resistance in the leafminer populations studied.
Therefore, glutathione-S-transferases seem to be of minor importance
as an abamectin resistance mechanism in Brazilian populations of T.
absoluta.
1. Introduction
Brazil is the eighth greatest producer of tomatoes in the
world, with 60,000 ha of the crop grown annually, and an
average productivity of 44 t.ha-1 (FAO, 1994). Tomato production for fresh consumption is the most important source of
income for small producers in several regions of the country.
However, this vegetable crop is often severely damaged by
pests in the tropics, and pesticides are intensively used to
control insects and pathogens in Brazil (Gravena, 1991;
Makishima, 1991; PicancËo et al., 1998). This situation substantially increases the crop production cost and leads to human
health and environmental problems in addition to selecting for
resistance to pesticides. The tomato leafminer, Tuta (=Scrobipalpuloides) absoluta (Meyrick) (Lepidoptera: Gelechiidae), is
considered to be one of the most important pests of tomato
production in Brazil (Souza and Reis, 1986; Souza et al., 1992).
It is an oligophagous insect, distributed throughout the Neotropical region, attacking solanaceous plants. It is of major
importance in Venezuela, Colombia, Chile, Equator, Bolivia,
Argentina, Peru (Povolny, 1975), and Uruguay (Carballo et al.,
1981). Its occurrence has been reported even in Japan (Nakano
and Paulo, 1983).
It has been a serious problem to tomato production in Brazil
since its introduction and rapid spread in the 1980s. The
damage caused by T. absoluta resembles that caused by other
Gelechiidae such as Keiferia lycopersicella (Wals.) in Central
and North America, and Phthorimaea operculella (Zell.) in the
Americas, Europe, Africa and Asia (Sannino and Nicodemo,
1979; Juvick et al., 1982; Abbas et al., 1993; Ebora et al., 1994;
Pouey et al., 1994). At high densities it can cause severe yield
losses (Souza et al., 1992; PicancËo et al., 1998).
Chemical control has been the primary control strategy for
this insect since the early 1980s (Souza and Reis, 1986), with
some farmers still making up to 36 insecticide applications
during the crop cycle (PicancËo et al., 1995). Producers have
observed insecticide failures in controlling this pest and
researchers have shown reduced insecticide activity in the field
(Souza et al., 1992; FrancËa, 1993; Guedes et al., 1994),
suggesting the development of resistant populations to compounds used against T. absoluta (GoncËalves et al., 1994).
Abamectin was first used around 1990 due to control failures
with other insecticides (Castelo Branco, 1990). Studies on
abamectin resistance in T. absoluta populations have not yet
been carried out, despite reports of resistance in this species to
other insecticides in Chile (Salazar and Araya, 1997). However,
studies on abamectin resistance have been carried out in
resistant strains of house flies (Musca domestica L.) (Roush and
Wright, 1986), German cockroaches (Blattella germanica (L.))
(Cochran, 1990, 1994), Colorado potato beetle (Leptinotarsa
decemlineata (Say)) (Argentine and Clark, 1990; Argentine et
al., 1992), and spider mites (Tetranichus urticae Koch and T.
mcdanuli McGregor) (Campos et al., 1995; Beers et al., 1998).
No cross-resistance (i.e., resistance to two or more insecticides
due to the same mechamism) to abamectin was detected in
these studies (Clark et al., 1995). Among lepidopteran pests,
only the diamondback moth, Plutella xylostella, has been
subjected to more intense investigation of abamectin resistance
(Abro et al., 1988; Iqbal and Wright, 1997). Resistance
mechanisms to abamectin have been studied in a few species,
where several major resistance mechanisms and some minor
factors have been implicated (Clark et al., 1995).
The aim of this study was to survey abamectin
resistance in Brazilian populations of T. absoluta and to
assess the possible involvement of detoxification enzymes in
*To whom correspondence should be addressed. Fax: +55 (31)3899-2537; e-mail: [email protected]
248
H. A. A. Siqueira et al.
abamectin resistance using insecticide synergists in `in vivo’
assays.
2.
Material and methods
Five populations of T. absoluta from the State of Minas
Gerais, one from SaÄo Paulo State and another from Rio de
Janeiro State, were used in this study (Table 1). A field
population collected from UberlaÃndia County, State of Minas
Gerais, was used as an abamectin susceptible standard
population because it was obtained from a site where this
insecticide had not been used and it was reported as a
population susceptible to this insecticide in a previous investigation (Siqueira, 1999). Colonies of T. absoluta were established
from at least 200 larvae obtained from heavily infested leaves
from each sampling site. The individual populations were reared
on tomato plants of variety Santa Clara, without insecticide
exposure, enclosed in cages and maintained under greenhouse
conditions at a temperature and daylength varying from 22 to
288C and from 10 to 14 h respectively, during the study period.
The colonies were maintained for two generations in the
laboratory before starting the bioassays.
In vivo bioassays, using insecticide-impregnated filter paper
(9 cm diameter) placed in Petri dishes (9 cm diameter61.5 cm
height), were carried out. Technical grade abamectin (Novartis
BiocieÃncias, SaÄo Paulo, SP) was used in the investigation. The
three synergists used were diethyl maleate, piperonyl butoxide
and triphenylphosphate (Aldrich Chemical Co., Milwauke, WI,
USA). Diethyl maleate is an inhibitor of glutathione-S-transferases, while piperonyl butoxide and triphenylphosphate are
inhibitors of cytochrome P450-dependent monooxygenases and
Table 1.
Origin and year of collection of leafminer populations ( T.
absoluta)
County
State
Araguari
Minas Gerais
Guiricema
Minas Gerais
Lavras
Minas Gerais
UberlaÃndia
Minas Gerais
VicËosa
Minas Gerais
SaÄo JoaÄo da Barra Rio de Janeiro
PaulõÂnia
SaÄo Paulo
Table 2.
Population
UberlaÃndia
PaulõÂnia
Guiricema
SaÄo JoaÄo da Barra
VicË osa
Lavras
Araguari
a
Local
Month/
Collection year
Field
Field
Field
Field
Field
Greenhouse
Greenhouse
08/1998
09/1998
08/1998
04/1998
10/1997
08/1997
08/1998
3.
Results
The concentration±mortality regression lines were obtained
for all combinations of insecticide or insecticide + synergist and
every insect population under study (tables 2±5). There was
significant variation on the susceptibility among the insect
populations studied in response to abamectin. The resistance
ratios were calculated by dividing the LC 50 of the most
susceptible population (UberlaÃndia) to this insecticide by the
LC 50 of the other insect populations (table 2). The LC 50 of the
susceptible population was significantly smaller than those of
the other populations based on the criterion of failure of 95% CL
to overlap (table 2). The resistance ratio among the resistance
populations ranged from 5.2- to 9.4-fold. Slopes of the
concentration±mortality curves for abamectin were relatively
similar among the different insect populations, showing similar
homogeneity of response for all populations.
Piperonyl butoxide synergized abamectin for all populations,
based on the criterion cited above, except for the UberlaÃndia
population which was slightly antagonized. Resistance suppression was complete for the PaulõÂnia population, and nearly
complete for the remaining populations (table 3). Diethyl maleate
Relative susceptibility of populations of tomato leafminer (Tuta absoluta) to abamectin
n
Slope+SEM
360
361
360
420
421
360
360
0.80+0.10
0.76+0.12
0.67+0.06
0.45+0.03
0.49+0.04
0.67+0.08
0.63+0.09
LC 50 resistant/LC 50 susceptible.
NS, not significant.
esterase respectively (Raffa and Priester, 1985; Bernard and
PhilogeÁne, 1993).
Three replicates with 20 second instar larvae of T. absoluta
were used at each insecticide concentration. For each concentration±mortality regression line, six to seven different insecticide
concentrations were applied; a control treatment of acetone
alone was included and used for correcting mortality in the other
treatments. On each replicate of each concentration we used a
filter paper impregnated with 1 ml of insecticide dissolved in
acetone. Insecticide concentrations were calculated as mg a.i./
cm2 of treated surface. Insects were counted as dead if they
were unable to walk. The synergist bioassays followed the same
methodology described above using a insecticide:synergist
proportion of 1:10. The synergists were applied on filter paper
with dried insecticide residues at the specified concentration,
where 1 ml of the synergist solution proportional to each
insecticide concentration was applied. No mortality was observed in preliminary assays with the synergists used alone at
the highest concentrations used in this investigation when in
mixture with abamectin. Concentration±mortality data were
subjected to probit analysis (PROC PROBIT, SAS Institute,
1987).
LC 50 (95% CL)
(mg a.i./cm2)
0.97
5.00
5.87
5.96
6.76
8.31
9.09
(0.87 ± 1.09)
(4.21 ± 5.81)
(4.90 ± 6.96)
(4.51 ± 7.52)
(5.28 ± 8.37)
(7.10 ± 9.87)
(7.68 ± 10.92)
LC 90 (95% CL)
(mg a.i./cm2)
2.40
18.22
21.92
48.74
47.15
34.66
35.97
(1.99 ± 3.14)
(14.51 ± 25.09)
(16.78 ± 32.34)
(35.13 ± 76.67)
(34.80 ± 71.20)
(25.14 ± 56.57)
(25.33 ± 65.02)
Resistance
ratioa
Ð
5.16
6.04
6.14
6.97
8.57
9.37
2
w
4.34
3.30
2.80
1.19
1.93
0.48
6.79
P
0.36
0.51
0.59
0.95
0.86
0.98
0.15
NS
NS
NS
NS
NS
NS
NS
249
Abamectin resistanc e and synergis m in T. absoluta
Table 3.
Population
UberlaÃndia
PaulõÂnia
Guiricema
VicË osa
Lavras
Araguari
Relative susceptibility of populations of tomato leafminer (Tuta absoluta) to abamectin+ piperonyl butoxide (1:10)
n
Slope+SEM
360
340
360
360
360
340
361
1.25+0.11
1.04+0.21
1.75+0.19
1.22+0.23
0.89+0.08
1.40+0.20
0.61+ 0.07
LC 50 (95% CL)
(mg a.i./cm2)
1.30
1.24
1.94
1.68
2.04
1.58
2.70
(1.19 ± 1.42)
(1.04 ± 1.40)
(1.65 ± 2.24)
(1.53 ± 1.84)
(1.77 ± 2.31)
(1.44 ± 1.72)
(2.08 ± 3.30)
Resistance
ratioa
Synergism
ratio b
w
Ð
0.75
4.03
3.03
3.55
3.31
5.26
3.37
2.51
5.47
8.74
4.68
5.53
3.18
3.21
0.95
1.49
1.29
1.57
1.22
2.08
2
P
0.64
0.32
0.07
0.24
0.24
0.53
0.52
NS
NS
NS
NS
NS
NS
NS
a
Resistance Ratio (= LC 50 synergized resistant /LC 50 synergized susceptible).
Synergism Ratio (= LC 50 unsynergized abamectin/ LC 50 synergized abamectin).
b
Table 4.
Population
UberlaÃndia
PaulõÂnia
Guiricema
VicË osa
Lavras
Araguari
Relative susceptibility of populations of tomato leafminer (Tuta absoluta) to abamectin + diethyl maleate (1:10)
n
Slope+SEM
366
367
400
362
360
360
363
1.47+0.20
0.83+0.04
0.55+0.08
1.01+0.14
0.89+0.10
1.34+0.17
0.89+0.08
LC 50 (95% CL)
(mg a.i./cm2)
1.84
4.03
4.84
2.73
2.52
2.19
6.30
(1.68 ± 1.99)
(3.45 ± 4.63)
(3.97 ± 6.07)
(2.43 ± 3.05)
(2.18 ± 2.86)
(2.01 ± 2.39)
(5.43 ± 7.13)
Resistance
ratio a
Synergism
ratio b
w
Ð
0.53
1.24
1.21
2.18
2.68
3.79
1.44
4.49
5.12
8.89
6.23
4.56
5.22
3.80
2.19
2.63
1.48
1.37
1.19
3.42
2
P
0.34
0.28
0.11
0.18
0.34
0.27
0.43
NS
NS
NS
NS
NS
NS
NS
a
b
Table 5.
Population
UberlaÃndia
PaulõÂnia
Guiricema
VicË osa
Lavras
Araguari
Relative susceptibility of populations of tomato leafminer (Tuta absoluta) to abamectin + triphenylphosphate (1:10)
n
Slope+SEM
343
361
360
363
360
366
362
0.89+0.30
0.57+0.08
0.71+0.08
0.76+0.09
0.64+0.08
1.29+0.19
0.67+0.05
LC 50 (95% CL)
(mg a.i./cm2)
1.95
2.18
4.06
2.28
2.17
2.21
5.06
(1.67 ± 2.25)
(1.65 ± 2.70)
(3.37 ± 4.77)
(1.91 ± 2.65)
(1.71 ± 2.61)
(2.02 ± 2.42)
(4.12 ± 6.03)
Resistance
ratio a
Synergism
ratio b
w
Ð
0.50
2.29
1.45
2.61
3.12
3.76
1.80
6.70
7.05
1.30
1.88
6.16
5.09
2.82
1.12
2.08
1.17
1.11
1.13
2.60
2
P
0.15
0.76
0.86
0.13
0.19
0.28
0.59
NS
NS
NS
NS
NS
NS
NS
a
b
synergized significantly the populations from Araguari, Lavras,
SaÄo JoaÄo da Barra and VicËosa; however, it had no effect on the
populations from PaulõÂnia and Guiricema and even antagonized
abamectin in the UberlaÃndia population at its LC50. Resistance
suppression was smaller than with piperonyl butoxide for the
Araguari, Lavras, SaÄo JoaÄo da Barra and VicËosa populations
(table 4). There was no resistance suppression for the PaulõÂnia
and Guiricema populations. Triphenylphosphate synergized all
populations, except the one from UberlaÃndia, in which a slight
antagonism to abamectin was observed (table 5). This synergist
completely suppressed abamectin resistance in four populations
and nearly did so in the remaining two among the six tested
populations.
Synergising insecticides usually results in steeper concentration±response curves if the population is heterogeneous for
resistance. This was generally the case in our study, which is
expected for field-collected populations. However there were a
few exceptions, mainly for triphenylphosphate, where no change
in slope was observed probably reflecting a higher homogeneity
of response to this synergist in the populations studied.
4. Discussion
T. absoluta resistance to abamectin was reported by
Siqueira (1999). The occurrence of this phenomenon in different
populations of this pest was suspected as a result of its
widespread use, usually in a mixture with mineral oil (Guedes et
al., 1995; Castelo Branco and FrancËa, 1996; Castelo Branco et
al., 1996). The low levels of resistance to abamectin observed in
our study suggest that the importance of mineral oil in the
250
H. A. A. Siqueira et al.
evolution of abamectin resistance in T. absoluta is probably
overestimated, even though it does provide support for the
contention that abamectin resistance is one of the causes of
control failures of this insecticide observed in field. The intensive
use of abamectin in T. absoluta control programmes seems not
to have been enough to select highly resistant strains. This is
probably due to the low dose of abamectin used in the field and
its fast degradation in the environment without bioaccumulation
which do not seem to provide strong selection pressure for
resistance (Clark et al., 1995).
Besides using enzymes to maintain their normal homeostasis, insects may also use them for protection against
xenobiotics. Among the known insecticide resistance mechanisms, it is not surprising that enhanced activity of detoxification
enzymes is one of the most common mechanisms of resistance
to insecticides (Scott, 1990a). Insect detoxification enzymes are
important resistance mechanisms and synergists are helpful in
providing preliminary evidence of their involvement as resistance mechanisms (Brindley and Selim, 1984; Scott, 1990b;
Bernard and PhilogeÁne, 1993; Ishaaya, 1993). In this study,
abamectin toxicity was enhanced by the synergists diethyl
maleate, piperonyl butoxide and triphenyl phosphate which
respectively inhibit the detoxification enzymes glutathione-Stransferases, cytochrome P450-dependent monooxygenases,
and esterases (Raffa and Priester, 1985; Bernard and PhilogeÁne, 1993), providing some interesting information regarding
abamectin resistance mechanisms in this insect-species.
Piperonyl butoxide nearly completely suppressed the resistance to abamectin in all populations, except for the PaulõÂnia
population of T. absoluta where the suppression was complete.
The synergism to abamectin by piperonyl butoxide suggests an
enhanced cytochrome P450-dependent monooxygenase activity
in this insect species as an abamectin resistance mechanism.
This effect by piperonyl butoxide has been observed in other
arthropod species. The involvement of monooxygenases in
abamectin resistance was observed in Colorado potato beetle,
house flies, two-spotted spider mites, Spodoptera littoralis and
Helicoverpa armigera (Scott, 1989; Christie and Wright, 1990;
Argentine et al., 1992; Campos et al., 1996).
Gluthatione-S-transferases are also probably involved in
abamectin resistance in T. absoluta. Our results indicate partial
suppression of abamectin resistance by diethyl maleate which
inhibit gluthatione-S-transferases. However this seems to be a
mechanism of minor importance. Argentine et al. (1992) found
that gluthatione-S-transferases were not important as a resistance mechanism in L. decemlineata and carboxylesterases
possibly play an important role in abamectin resistance in this
species. Despite the occurrence of partial suppression by diethyl
maleate in the populations from PaulõÂnia and Guiricema, the
synergistic effect was not significant. Triphenylphosphate and
piperonyl butoxide are stronger synergists to abamectin than
diethyl maleate suggesting enhanced detoxification by esterases and cytochrome P450-dependent monooxygenases in
populations of T. absoluta resistant to abamectin.
Triphenylphosphate completely suppressed abamectin resistance in four T. absoluta populations (from Lavras, PaulõÂnia,
SaÄo JoaÄo da Barra, and VicËosa) and provided partial suppression in two populations (from Araguari and Guiricema). These
results suggest a major involvement of esterases as an
abamectin resistance mechanism in Brazilian populations of T.
absoluta, with cytochrome P450-dependent monooxygenases
probably playing a secondary role in addition to gluthatione-Stransferases as a mechanism of minor importance. The
coexistence of different resistance mechanisms in the same
insect populations suggests an oligo or polygenic basis for
abamectin resistance in these populations.
The use of synergists in insecticide resistance management
programmes has been frequently suggested (e.g. Oppenoorth,
1985; Guedes, 1991; Denholm and Rowland, 1992; Bernard and
PhilogeÁne, 1993). However they may not be useful for managing
abamectin resistance in Brazilian populations of T. absoluta,
because of the likely occurrence of multiple resistance mechanisms. Nonetheless, synergists can be important tools for
managing T. absoluta populations lacking insecticide crossresistance. Resistance to abamectin is polyfactorial in both L.
decemlineata and M. domestica, which has resulted in several
major resistance mechanisms (e.g. excretion, oxidative metabolism, penetration) and minor factors (e.g. altered target site,
conjugation, esteratic hydrolysis/sequestration) associated with
the phenomenon (Clark et al., 1995). The resistance to
abamectin in T. absoluta populations may be oligo- or even
polyfactorial, but further investigations are necessary to better
assess this possibility.
Acknowledgements
We would like to express our gratitude Nilton C. Picinato
(DuPont) and Norma E. Pereira (Universidade Estadual do
Norte Fluminense) for providing the T. absoluta population from
PaulõÂnia (SP) and SaÄo JoaÄo da Barra (RJ) respectively; and
Novartis BiocieÃncias for providing the technical grade abamectin
used in this study. Financial support was provided by FAPEMIG,
CNPq and CAPES and is acknowledged here.
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January - February 2005
Neotropical Entomology 34(1)
113
CROP PROTECTION
Insecticide Resistance in Argentine Populations of Tuta absoluta (Meyrick)
(Lepidoptera: Gelechiidae)
MARCELA M.M. LIETTI1, EDUARDO BOTTO2 AND RAÚL A. ALZOGARAY3
Cátedra de Zoología Agrícola, Facultad de Ciencias Agrarias, Universidad Nacional de Rosario (U.N.R.)
C.C. 14, (S2125ZAA) Zavalla, Santa Fe, Argentina. E-mail: [email protected]
2
Insectario de Investigaciones para Lucha Biológica, IMYZA-CNIA, INTA. C.C. 25, (1712)
Castelar, Buenos Aires, Argentina
3
Centro de Investigaciones de Plagas e Insecticidas (CIPEIN-CITEFA/CONICET)
J. B. de La Salle 4397, (B1603ALO) Villa Martelli, Buenos Aires, Argentina
E-mail: [email protected]
1
Neotropical Entomology 34(1):113-119 (2005)
Resistência a Inseticidas em Populações Argentinas de Tuta absoluta (Meyrick) (Lepidoptera: Gelechiidae)
RESUMO - A traça-do-tomateiro, Tuta absoluta (Meyrick), é uma das pragas chaves no tomateiro na
Argentina. O controle químico tem sido o principal método de controle empregado a partir da sua
dispersão nos anos 70. Contudo, tem-se observado uma redução na eficácia de alguns dos inseticidas
recomendados a partir da década de 80. O objetivo deste trabalho foi estudar a toxicidade de três
inseticidas amplamente usados no controle químico de T. absoluta (abamectina, deltametrina e
metamidofós) em larvas de uma população susceptível de laboratório (CASTELAR) e duas populações
colectadas em casa de vegetação (ROSARIO e BELLA VISTA). Inseticidas foram diluídos em acetona
e aplicados topicamente na região dorsal mediana do abdome de larvas no segundo dia do quarto
estágio larval. Para cada inseticida estimou-se o LD50 e calculou-se o Nível de Resistência (NR = LD50 de
cada população de casa de vegetação/LD50 população de laboratório). As populações de ROSARIO e
BELLA VISTA mostraram os seguintes NRs: > 68.38 para deltametrina; 2.48 e 3.49 para abamectina,
respetivamente; e 0.79 e 0.86 para metamidofós, respetivamente. A resistência a deltametrina observada
em ROSARIO pode ser resultante da alta pressão seletiva exercida pelos piretróides nessa localidade.
A resistência incipiente a abamectina detectada em BELLA VISTA pode ter sido causado pelo uso
freqüente do inseticida nessa localidade ou pode estar associada à variação natural.
PALAVRAS-CHAVE: Traça-do-tomateiro, deltametrina, abamectina, metamidofós, resistência a inseticidas
ABSTRACT - The tomato leafminer, Tuta absoluta (Meyrick), is one of the key pests of tomato in
Argentina. Since its dispersal in the 1970s, chemical control has been the main method of controlling it.
However, reduced efficacy of some of the recommended insecticides has been observed since the
1980s. The aim of this work was to study the toxicity of three insecticides widely used in chemical
control of T. absoluta (abamectin, deltamethrin and methamidophos) on larvae from a laboratory
susceptible population (CASTELAR) and two greenhouse populations (ROSARIO and BELLA VISTA).
Insecticides were dissolved in acetone and topically applied to the mid-dorsal abdominal region of twoday old 4th instar larvae. LD50 values were estimated and the Resistance Ratio (RR) for each insecticide
was calculated (RR = LD50 value of each greenhouse population/LD50 value of the susceptible
population). ROSARIO and BELLA VISTA populations showed the following RRs values: > 68.38 for
deltamethrin; 2.48 and 3.49 for abamectin, respectively; and 0.79 and 0.86 for metamidophos, respectively.
Deltamethrin resistance observed in ROSARIO could be due to the high selective pressure exerted by
pyrethroids in this location. Deltamethrin resistance in BELLA VISTA is more difficult to explain,
because pyrethroids were scarcely used in the greenhouse where the insects were sampled. The incipient
abamectin resistance detected in the BELLA VISTA population could result from the frequent use of
this insecticide in this location, although natural variation can not be discarded.
KEY WORDS: Tomato leafminer, deltamethrin, abamectin, metamidophos, insecticide resistance
114
Lietti et al.
Insecticide Resistance in Argentine Populations of Tuta absoluta (Meyrick)...
Tomato crop is the second horticultural crop in Argentina,
with a harvested area of 24,000 ha and an average yield of
30,833 kg/ha (FAO 1996). Seventy per cent of the production
destination is for consumption in natura and the rest is
industrialized (Gómez Riera 1992). Tomato produced under
greenhouses as well as in outdoor areas for consumption in
natura brings the highest gross financial return to farmers in
the Litoral Region (Buenos Aires, Corrientes and Santa Fe
provinces) (Stoppani & Rodríguez 1992).
The tomato leafminer, Tuta absoluta (Meyrick), is a
neotropical oligophagous insect, which attacks solanaceous
crops. Since the 1960s it has become one of the key pests of
tomato crops in many South American countries (Souza et
al. 1983, Larraín 1986, IAN 1994). A fruit importation from
Chile may have introduced it to Mendoza province
(Argentina) in April 1964 (Bahamondes & Mallea 1969);
dissemination to other tomato production regions occurred
through fruit commercialization (Benavent et al. 1978, Cáceres
1992, Riquelme 1993).
Larvae can damage tomato plants during all growth stages,
producing large galleries in their leaves, burrowing stalks,
apical buds, green and ripe fruits (Cáceres 1992, IAN 1994). It
can cause important yield losses in different production
regions and under diverse production systems (Benavent et
al. 1978, Cáceres 1992).
Since its introduction, chemical control has been the main
method of control used against T. absoluta in all production
regions in Argentina. Horticultural growers have tried to
decrease its injure applying insecticides two times a week
during a single cultivation period. Effective chemical control
was difficult to achieve because of the mine-feeding
behaviour of larvae, lack of a threshold action, and deficient
spraying technology.
Initially, the only insecticides used against tomato
leafminer in Argentina were organophosphates, which were
gradually replaced by pyrethroids during the 1970s. In the
early 1980s, cartap, alternated with pyrethroids, and
thiocyclam were introduced with the former showing excellent
efficacy at that moment. During the 1990s, insecticides with
novel sites of action such as abamectin, acylurea insect
growth regulators, spinosad, tebufenozide and chlorfenapyr
were introduced (Galarza & Larroque 1984, Polack 1999,
Cáceres 2000).
Reports of insecticide resistance development in
populations of T. absoluta were scarce. A decrease in the
control efficiency of organophosphorous insecticides was
observed in Bolivia and Chile, which could be satisfactorily
controlled by pyrethroids (Moore 1983, Larraín 1986).
Recently, the existence of resistance to organophosphates
and pyrethroids in Chile (Salazar & Araya 1997, 2001) and to
abamectin, cartap, methamidophos and permethrin in Brasil
(Siqueira et al. 2000, 2001) were reported.
The suspicion about the development of resistance in
Argentine populations of T. absoluta has been present since
the 1980s, when growers and agronomic advisers observed
that some of the compounds recommended for its control
were loosing its effectiveness in the field. Apparently, the
loss in effectiveness has not occurred with the same intensity
and to the same compounds in all tomato producing regions.
Nevertheless, the susceptibility of different populations to
distinct active ingredients has not yet been determined.
Owing to a decreasing activity of some insecticides used
against T. absoluta and the report of resistant populations
in Chile and Brasil, it is necessary to detect and quantify
the resistance to the main insecticides used for its control
in Argentina.
The objective of this work was to evaluate the toxicity
of abamectin, deltamethrin and methamidophos to a
laboratory-susceptible and two greenhouse populations of
T. absoluta, in order to establish if insecticide resistance
has developed in the last ones. The three insecticides used
in this study are currently registered and widely used by
farmers as chemical control of T. absoluta and other tomato
pests in Argentina (CASAFE 2001).
Material and Methods
Biological Material. A susceptible population of T. absoluta
(CASTELAR population), reared since 1993 without
exposure to insecticides, was provided by the Insectario de
Investigaciones para Lucha Biológica, IMIZA, CNIA-INTA.
(Castelar, Buenos Aires Province).
Greenhouse individuals of T. absoluta were collected
from tomato crops cultivated in the Módulo Experimental
de Nuevas Tecnologías (Rosario, Santa Fe Province)
(ROSARIO population) and in the Experimental Station,
INTA (Bella Vista, Corrientes Province) (BELLA VISTA
population). Both populations came from experimental
crops grown under greenhouses and exposed to intense
chemical treatments to maintain them free of pests. The
greenhouses are made of wood and covered by plastic.
The sides of them are lifted, whenever required, for
regulating the temperature inside it. Information about
insecticides used in each site during the current cultivation
period was obtained. Individuals from both the susceptible
and the greenhouse populations were separately reared
on greenhouse organically-grown tomato plants
(Lycopersicon esculentum Mill) cv. Presto (Petoseed ®)
in a controlled environment room at 25 ± 2°C and under a
photoperiod of 14:10 L:D. The experimental work was done
on two-day old 4th larval stage.
Chemicals. The insecticides used in this study were
abamectin 94% (Chemotecnica, Argentina), deltamethrin >
99% (Roussell-Uclaf, France) and methamidophos 68%
(Bayer, Argentina). Acetone pro-analysis (Merck,
Argentina) was used as solvent.
Bioassay. Insecticides were topically applied to the middorsal abdominal region of the larvae using a micro syringe
provided with a dispenser. Each insect received 0.2 µl of a
solution of insecticide in acetone. Control groups were
topically treated with acetone alone. Five to seven doses of
each compound and 15 to 20 larvae for each dose were used
to estimate the Lethal Dose 50% (LD50) values. Three to
five independent replicates for each bioassay were done.
Data of the different replicates were pooled when the
confidence limits of their respective LD50 overlapped.
115
99
99
98
98
Discussion
There are very few studies of insecticide resistance in T.
absoluta. Salazar & Araya (1997) reported resistance to
deltamethrin, metamidophos, esfenvalerate, lambdacyhalothrin and mevinphos in Chilean populations of this
pest. Studying different larval stages from several localities,
they found RRs values ranging from 2.2 to 8.2 for deltamethrin,
from 1.6 to 3.9 for metamidophos, from 1.9 to 12.6 for
33 22
90
90
80
80
70
70
60
60
50
50
40
40
30
30
CASTELAR
(1) (1)
CASTELAR
ROSARIO
(2) (2)
ROSARIO
BELLA
VISTA
(3) (3)
BELLA
VISTA
20
20
10
0.1
0,1
Results
1.01,0
10.010,0
dose
Dose(µg/insect)
( �g/insect)
98
98
CASTELAR
(1)(1)
CASTELAR
ROSARIO
(2)(2)
ROSARIO
BELLA
VISTA
(3)(3)
BELLA
VISTA
95
95
90
90
Mortality (%)
mortality
(%)
Fig. 1 shows the dose-response relationship for abamectin
and metamidophos in an insecticide susceptible
(CASTELAR) and two greenhouse populations (BELLA
VISTA and ROSARIO) of T. absoluta. The DL50 and RRs
values are shown in Table 1. The LD50 value of deltamethrin
was 0.35 µg/larva for the CASTELAR population. The LD50
values of deltamethrin could not be calculated for the BELLA
VISTA and ROSARIO populations because the highest dose
applied (24 mg/larva, which is near the solubility limit of the
insecticide) caused only 31.9 and 18.3% of mortality,
respectively. The RRs values were > 68.4 in both cases,
indicating a high resistance to deltamethrin.
The LD50 values of methamidophos were 0.81, 0.70 and
0.65 µg/larva for the CASTELAR, BELLA VISTA and
ROSARIO populations, respectively. No significant
differences among those values were observed (P > 0.05).
The RRs values were not significantly different from 1 (P >
0.05). Hence, no resistance to this insecticide was observed
in the greenhouse populations.
The LD50 values of abamectin were 0.16, 0.57 and 0.41 ηg/
larva for the CASTELAR, BELLA VISTA and ROSARIO
populations, respectively. The BELLA VISTA LD50 value was
significantly higher than the CASTELAR one (P < 0.05), but
there was no significant difference between the ROSARIO
and CASTELAR values (P > 0.05). BELLA VISTA and
ROSARIO RRs were 3.49 and 2.48, respectively. Both values
differed significantly from 1 (P < 0.05). These results indicated
a slight resistance to abamectin in the BELLA VISTA
population.
11
Metamidophos
metamidophos
95
95
Mortality (%)
mortality
(%)
After treatment, the larvae were individually placed in 3 cm3
plastic vials (13 x 35 mm) in a controlled environment room at 27
± 2°C and under a photoperiod of 14:10 (L:D). Mortality was
recorded 24h after treatment under stereoscopic microscope (10x).
Larvae were considered as dead when they were not able to
move back to ventral position after being placed on their dorsum.
The LD50 values were calculated using the Probit method
(Lichtfield & Wilcoxon 1949). In all cases, differences between
values were considered significant (P < 0.05) if the respective
95% confidence limits did not overlap.
Resistance Ratios (RRs) values were calculated by
dividing the LD50 value of each greenhouse population by
the LD50 value of the susceptible population. Confidence
limits of RRs were calculated according to Robertson &
Preisler (1992). RRs were considered significantly different
from 1 (P < 0.05) when their 95% confidence limits did not
include 1.
80
80
70
70
60
60
50
50
40
40
30
30
20
20
10
11
0,01
0,01
2
2
33
0,10
0,10
Abamectin
abamectin
1,00
1,00
10,00
10,00
Dose
(ng/insect)
dose
(ng/insect)
Figure 1. Dose-response regressions for metamidophos
and abamectin topically applied on T. absoluta 4th larval stage
from a laboratory (CASTELAR) and two greenhouse
populations (ROSARIO and BELLA VISTA).
esfenvalerate, from 1.8 to 11.5 for lambda-cyhalothrin, and
from 1.9 to 5.5 for mevinphos. Later, Salazar & Araya (2001)
found higher RRs values for the same insecticides in other
populations of T. absoluta.
Resistance to abamectin, cartap, methamidophos and
permethrin was reported in several Brazilian populations of
T. absoluta (Siqueira et al. 2000). The RRs values varied from
5.2 to 9.4 for abamectin, from 2.2 to 21.9 for cartap, from 2.6 to
4.2 for metamidophos, and from 1.9 to 6.6 for permethrin. In
other study, Siqueira et al. (2001) studied the toxicity of
abamectin, with and without synergists, to six abamectin
resistant populations of T. absoluta. A complex result was
116
Lietti et al.
Table 1. Susceptibility of Argentine populations of the tomato leafminer, T. absoluta, to insecticides.
Insecticide
Population
n
Slope
± SE
Deltamethrin
CASTELAR
479
0.88 ± 0.13
115
130
230
---
Methamidophos
ROSARIO
BELLA VISTA
CASTELAR
4.42 ± 0.45
ROSARIO
222
1.85 ± 0.44
BELLA VISTA
146
4.16 ± 0.45
CASTELAR
348
0.97 ± 0.12
ROSARIO
324
1.35 ± 0.19
BELLA VISTA
188
1.43 ± 0.29
Abamectin
LD 50
(95% CL) 1
µg a.i./larva
0.35
(0.22 – 0.55)
> 24.00
> 24.00
0.81
(0.65 – 0.96)
0.65
(0.21 – 1.06)
0.70
(0.55 – 0.85)
ηg a.i./larva
0.16
(0.09 – 0.27)
0.41
(0.23 – 0.62)
0.57 4
(0.28 – 0.92)
Resistance Ratio 2
(95% CL)1
χ2
3.06
NS 3
--2.12
NS
1.06
NS
0.71
NS
-> 68.38
> 68.38
-0.79
(0.40 – 1.60)
0.86
(0.65 – 1.5)
4.83
NS
0.98
NS
1.47
NS
-2.48 5
(1.22 – 5.02)
3.49 5
(1.64 – 7.42)
95% CL = 95% confidence limits; 2Resistance ratio = LD50 greenhouse population/LD50 laboratory population; 3NS = No significant;
Significantly different from the laboratory-susceptible population (CASTELAR) (P < 0.05); 5Significantly different from 1 (P < 0.05).
1
4
obtained: piperonyl butoxide (an inhibitor of the mixed
function microsomal oxidases activity —MFMO—)
suppressed the abamectin resistance completely in only one
population and partially in the rest; triphenylphosphate (an
inhibitor of the esterase activity) suppressed completely the
abamectin resistance in four populations; diethyl maleate (an
inhibitor of the glutathion S-transferase activity) suppressed
partially the resistance in nearly all populations. These results
suggested to the authors that the resistance to abamectin in
T. absoluta populations may be oligo or even polyfactorial,
and that several genes should be involved.
In this work, the existence of insecticide resistance in
Argentine populations of T. absoluta has been experimentally
demonstrated for the first time. Deltamethrin resistance was
observed in the two populations studied (ROSARIO and
BELLA VISTA), and a weak resistance to abamectin was
observed just in one of them (BELLA VISTA).
Deltamethrin is an insecticide widely used in the Horticultural
Belt of Rosario city (where the ROSARIO population was
collected). We found a high level of resistance (> 68.4) to
deltamethrin in individuals from the ROSARIO population. In
75% of cases, pyrethroids (deltamethrin or lambda-cyhalothrin)
were sprayed before our sampling (Table 2). The deltamethrin
resistance observed could be due to the high selective pressure
exerted by pyrethroids on this population.
Abamectin was introduced for tomato leafminer control
in the Horticultural Belt of Rosario city in the 1990s to
overcome the decrease of cartap efficacy. The ROSARIO
population received no application of abamectin, neither
before the insects collection nor in recent previous years
(Table 2). We found no significant differences between the
LD50 values of this insecticide evaluated on the ROSARIO
and CASTELAR populations.
Metamidophos is a broad spectrum systemic insecticide
used by the farmers in the Horticultural Belt of Rosario city
only during the vegetative growth stage of tomato because of
its pre-harvest interval of 10 days. The lack of resistance to
metamidophos in the ROSARIO population could be due to
the scarce use of this compound in the sampling site (Table 2).
Deltamethrin was ineffective to control the tomato
leafminer in the Experimental Station of Bella Vista city as
resulted from efficacy assays carried out in the period 1981
to 1987 (Cáceres 1992), when this pest began to compromise
tomato production in this location. However, deltamethrin is
used by farmers to control several tomato and pepper pest
species (9.5% of the total number of sprays per cultivation
cycle) (S. Cáceres, personal communication). The total number
of sprays received by the BELLA VISTA population before
Table 2. Insecticides applied to control the ROSARIO
population of T. absoluta before the insects were collected
for this study. Módulo Experimental de Nuevas Tecnologías,
Rosario, Santa Fe.
Months
(year 2000)
June to
October
July to
November
July
Insecticide
Deltamethrin
Number of
applications
7
Commercial
name
Decis 5
Lamdbacyhalotrin
Methamidophos
5
Karate
1
Tamaron
August
Cartap
1
Padam 50 SP
September
and October
Imidacloprid
2
Confidor
the insect collection was 11, with seven applications of
abamectin (63.6%), three of imidacloprid (27.3%) and one of
deltamethrin (9%) (Table 3). During the two previous years,
deltamethrin was not used in the greenhouse where this
population was collected, but it was applied in other
greenhouses of the same Experimental Station.
In the BELLA VISTA population, a high deltamethrin
resistance (RR > 68.4) was observed, although this population
received a relatively low number of pyrethroids applications.
This result is more difficult to explain. Deltamethrin was used
in other greenhouses in the Horticultural Belt of Bella Vista,
so resistance could be due to migration. An incipient
abamectin resistance was observed in BELLA VISTA (see
below), so an alternative explanation is that deltamethrin
resistance is due to cross-resistance after abamectin selective
pressure. Pyrethroids and abamectin have different sites of
action, however, a common metabolic detoxification
mechanism could confer resistance to both insecticide
groups. For instance, abamectin resistance in the Colorado
potato beetle, Leptinotarsa decemlineata (Say), largely
resulted from increased MFMO activity (Clark et al. 1994).
The involvement of MFMO in the resistance to deltamethrin
was also confirmed in Cidia pomonella (L.) after in vitro
metabolism studies (Sauphanor et al. 1997). Abro et al. (1988)
reported a cypermethrin resistant population of Plutella
xylostella (L.) which was also resistant to abamectin,
indicating that cross-resistance between pyretroids and the
latter is possible. The simultaneous application of piperonyl
butoxide was followed by partial reversion of the resistance
to deltamethrin in C. pomonella (Sauphanor et al. 1997).
Piperonyl butoxide also synergized abamectin in resistant
individuals of P. xylostella (Abro et al. 1988) and, as discussed
above, T. absoluta (Siqueira et al. 2001). These results suggest
that MFMO activity could be a mechanism of resistance to
both pyrethroids and abamectin.
Abamectin, in combination with mineral oil, was
introduced for chemical control of the tomato leafminer in
Bella Vista in 1994 and it is still effective in the field (Cáceres
2000). Abamectin has been used in the greenhouses of the
Experimental Station of Bella Vista before collecting the
BELLA VISTA population and during the last two years, and
a weak resistance to this compound (RR = 3.5) was observed.
It is possible that resistance is arising due to the selective
pressure exerted by the application of abamectin. Other
possibility is that the values observed are due to natural
variation (this can not be confirmed because in Argentina
Table 3. Insecticides applied to control the BELLA VISTA
population of T. absoluta before the insects were collected
for this study. Experimental Station, INTA, Bella Vista,
Corrientes.
Month
(year 2000)
April
May to
September
July to
September
Deltamethrin
Number of
applications
1
Commercial
name
Decis 5
Abamectin
7
Vertimec
Imidacloprid
3
Confidor
Insecticide
117
there is not a baseline of insecticide toxicity to T. absoluta).
Methamidophos was not used for chemical control of the
tomato leafminer in the Bella Vista Experimental Station, mainly
due to the relatively low efficacy of this compound in
comparison with abamectin (Cáceres 1992). Nevertheless,
metamidophos is used by growers to control several tomato
and pepper pest species (26.2% of the total number of sprays
per cultivation cycle on tomato and pepper) (S. Cáceres,
personal communication). The lack of usage in the sampling
site would explain that no resistance was observed for this
compound in the BELLA VISTA population (Table 3).
In the Litoral Region of Argentina, protected tomato
production offers a favorable environment for the
development of T. absoluta from May to August, providing
it with food and shelter. Moreover, since populations develop
faster in greenhouses than outdoors, the population level
and the consequent damage abruptly increase since early
October, which leads to early use of insecticides under
protected cultivation. The tomato leafminer has several
biological traits that favor resistance development. It has
many generations per year (more than five), which overlap in
protected crops, it has a relatively high fecundity (an average
of 40 to 55 eggs per female) and it survives in the soil at the
pupa stage (Botto 2000). The larvae and pupae are transported
form one region to another in infested containers and fruits,
allowing the mixing of individuals subjected to different
chemical regimens.
Although a rotation of different active ingredients was
done during each cultivation cycle in the two populations
studied, it was not aimed to manage resistance. The lack of
insecticide resistance management tactics favors resistance
development. The occurrence of resistant individuals under
greenhouses constitutes a potential danger. Taking into
account that the sides of the greenhouses are lifted whenever
required, for regulating the temperature inside them, the
resistant individuals might migrate outdoors in spring,
colonizing outdoor tomato crops. When insecticides are
applied, the resistant individuals have a biological advantage
in contrast with susceptible ones. This would contribute to
the development of resistance in outdoor tomato crops.
Resistance development is a consequence of insecticide
applications on an insect population and it must be
managed. Resistance management should be a component
of integrated pest management, which seeks to minimize
pesticide usage through the application of alternative
tactics such as cultural control and conservation of natural
control through selective insecticides. Monitoring the
susceptibility of different populations exposed to distinct
active ingredients is essential. The data obtained by means
of a monitoring plan should be used to design resistance
managing strategies, for example, the alternation of
insecticides with different modes of action and
detoxification, or the diminishing of conventional insecticide
use by employing alternative control tools. Several pests,
such as thrips and white flies, develop on tomato crops and
are sometimes controlled by the same compounds used
against the tomato leafminer. For this reason, insecticide
resistance management of T. absoluta should be considered
in the context of key-pest arthropod complexes of crops.
118
Acknowledgments
To the Centro de Investigaciones de Plagas e Insecticidas
for providing the technical grade insecticides deltamethrin
and abamectin. To Bayer Argentina for donating the technical
grade insecticide metamidophos. To Ing. Agr. Sara Cáceres
(E.E.A.INTA Bella Vista) for sending the T. absoluta
population from Bella Vista. To the two anonymous reviewers
for their helpful comments.
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Robertson, J.L. & H.K. Preisler. 1992. Pesticide bioassays
with arthropods. Boca Ratón, CRC Press, 127p.
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insecticidas en la polilla del tomate. Simiente 67: 8-22.
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L.O. Salgado. 1983. Controle da traça-do-tomateiro.
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protección en la región litoral sur del río Paraná
(República Argentina). Informe Técnico 61. Estación
Experimental Agropecuaria San Pedro, INTA, 47p.
Received 07/X/04. Accepted 07/X/04.
Volumen
26, Nº 1, Páginas 65-72
Efecto del imidacloprid en el control de la polilla del tomate (Tuta absoluta
Meyrick)
65
IDESIA (Chile) Enero - Abril 2008
EFECTO DEL IMIDACLOPRID EN EL CONTROL DE LA
POLILLA DEL TOMATE (TUTA ABSOLUTA MEYRICK)
EFFICACY OF IMIDACLOPRID TO CONTROL THE TOMATO BORER
(TUTA ABSOLUTA MEYRICK)
Marcelo Dante Collavino1; Rosana Alejandra Giménez2
RESUMEN
La grave incidencia de Tuta absoluta en la producción de tomate, el alto uso de plaguicidas para su control, el riesgo de contaminación del ambiente y la generación de resistencia hacen que sea muy importante encontrar formas alternativas de control eficiente
de esta plaga. Con el fin de evaluar la eficacia del imidacloprid en el control de la polilla del tomate, en distintas dosis y formas
de aplicación se desarrolló este ensayo en condiciones de invernáculo.
Para ello se prepararon dos diluciones del insecticida, que fueron aplicadas de dos formas: por riego y por inmersión de la raíz
del plantín con su pan de tierra.
Para evaluar el daño se realizó el cálculo del porcentaje de folíolos dañados por planta y el número de lesiones por hoja en distintos momentos desde la aplicación. El diseño fue factorial, completamente aleatorizado y con nueve repeticiones, aplicándose
ANOVA. Se comprobó que hay diferencias significativas entre las diluciones y también entre las dos formas de aplicación (riego
e inmersión). Siendo los tratamientos que mejor controlaron a la plaga: dilución al 3,5% aplicada por riego y dilución al 7%
aplicada por inmersión.
Palabras clave: Tuta absoluta, imidacloprid, riego, inmersión.
ABSTRACT
The incidence of Tuta absoluta in tomato production, the use of pesticides for its control, the risk of contamination to the environment and the creation of a generation of resistance, makes it very important to find alternative ways to efficiently control the
tomato borer. This test was developed under greenhouse conditions to assess the effectiveness of the imidacloprid to the control of
this pest at different rates and application forms. Two dilutions of the insecticide were prepared and applied in two different ways:
by watering and by the immersion of the root of the plants into the soil bed. To evaluate the damage, calculations were carried
out on the percentage of the leaves damaged on each plant and on the number of lesions on each leaf at different moments of the
application. The design was factorial, completely randomized and with 9 replications, and an ANOVA was carried out. Significant
differences were confirmed among the dilutions and also among the two application forms (watering and immersion). The better
treatments were: dilution of 3,5% applied by watering and dilution of 7% applied by immersion.
Key words: Tuta absoluta, imidacloprid, watering, immersion.
INTRODUCCIÓN
En el cultivo de tomate el tipo de producción más
tecnificado es el realizado bajo invernáculo, donde
el problema de la polilla del tomate (T. absoluta)
es mucho más grave que a campo (Ripa, 1981).
1
2
Dentro del invernáculo es menor la incidencia de
las bajas temperaturas, produciéndose condiciones
muy favorables para incrementar la incidencia de
esta plaga, que acorta su ciclo de vida y produce
muchas generaciones superpuestas a lo largo del
ciclo de cultivo.
Cátedra de Zoología Agrícola, Facultad de Agronomía, Universidad de Buenos Aires. Av. San Martín 4453, Buenos Aires
(CP C1417DSE), Argentina. E-mail: [email protected]
Cátedra de Terapéutica Vegetal, Facultad de Agronomía, Universidad de Buenos Aires. Ídem anterior. E-mail: rgimenez@
agro.uba.ar
Fecha de Recepción: 06 Marzo 2006
Fecha de Aceptación: 22 Octubre 2007
66
IDESIA (Chile) Volumen 26, Nº 1, Enero-Abril, 2008
T. absoluta (Lepidoptera; Gelechiidae) produce daños muy importantes al cultivo del tomate
en casi todas las zonas de producción hortícola de
Argentina (INTA, 1991). Las larvas lesionan el
follaje haciendo galerías dentro de las hojas que
pueden llegar a ocupar gran parte del área foliar.
También penetran en el fruto construyendo túneles
que al llenarse de excrementos causan la pudrición
y caída de los mismos (Betancourt, 1995). De esta
manera se pierde rendimiento y también disminuye
la calidad de los frutos obtenidos.
Los graves daños que esta plaga produce han
hecho que los productores aplicaran insecticidas
muy frecuentemente, generando resistencia a la
mayoría de los insecticidas utilizados, especialmente
hacia los fosforados (Larraín, 1986). En Argentina,
actualmente, están registrados numerosos productos
para el control de esta plaga: ciflutrina, cipermetrina, deltametrina, fenvalerato, lambdacihalotrina
y permetrina (piretroides), acefato, clorpirifós,
fenitrotión, metamidofós, piridafentión y triazofós
(organofosforados), abamectín y cartap (microbiológicos), clorfluazurón, lufenurón, metoxifenocide,
tebufenozide, teflubenzurón y triflumurón (IGR),
spinosad (Naturalyte) y tiociclán hidrogenoxalato
(nereistoxina) (CASAFE, 2001). Mientras que el
imidacloprid se encuentra registrado para aplicar en
el cultivo de tomate exclusivamente para controlar
moscas blancas (Bemisia tabaci, Trialeurodes spp. y
Aleurothripsus spp.) y minador del tomate (Faustinus
cubae) y trips (Frankliniella schultzei).
Otros investigadores han realizado estudios
para establecer la eficacia de insecticidas (Reis et
al., 1998; Lima y Machado, 1996) en aplicaciones
foliares para controlar T. absoluta.
El imidacloprid se caracteriza por tener un
modo de acción sistémico y de contacto, amplio
espectro de acción y posibilidad de ser absorbido
tanto por follaje como por raíces. Además, posee
un mecanismo de acción diferente al de la mayoría
de los insecticidas, por lo que no se han registrado
casos de resistencia en las plagas. Pertenece al
grupo de las nitroguanidinas y posee un efecto
residual de varias semanas y una baja toxicidad
para mamíferos, con una dosis letal media (DL 50)
oral aguda en rata 24 h de 450 mg/kg (CASAFE,
2001). Además, Epperlein et al. (1997) mostraron
que este insecticida aplicado al suelo no produjo
efectos adversos sobre artrópodos predadores de la
superficie del suelo.
Todas estas características hacen que sea posible
su aplicación mediante métodos no convencionales, haciendo tratamientos menos contaminantes
y más económicos, como serían las aplicaciones
localizadas, evitando la pulverización foliar en
cobertura total.
Así, con el fin de encontrar formas alternativas
de control eficiente de la polilla del tomate, evaluamos la aplicación de imidacloprid mediante riego
y por inmersión de raíces al trasplante.
MATERIALES Y MÉTODOS
El insecticida con que se realizó este trabajo es
el formulado comercial Confidor SL100 ® de Bayer,
cuyo ingrediente activo es el imidacloprid.
El cultivo fue realizado en un invernáculo de esta
Facultad, con tomate “platense común” y ejemplares
de T. absoluta criados en cámaras.
La cría de T. absoluta se realizó en jaulas con
luz artificial, sobre plantines de tomate cultivados
en macetas plásticas.
La siembra de tomate fue realizada en almácigos tipo speedling, con sustrato previamente
desinfectado con sulfato neutro de oxiquinoleina.
Estos almácigos se regaron periódicamente con
solución fertilizante N-P-K (15-15-15).
Se utilizaron 45 macetas plásticas de 25 cm
de diámetro, para realizar allí el trasplante de los
plantines.
Se prepararon dos diluciones del insecticida,
una al 3,5% y otra al 7%. Ambas fueron aplicadas
de dos formas distintas:
1) Riego de las macetas con regadera, un día antes
del trasplante. El riego se realizó hasta saturar
el suelo.
2) Inmersión de la raíz del plantín con su pan de
tierra, durante 10 seg. Una vez escurrida, el
plantín se trasplantaba a la maceta.
Quedan así determinados cinco tratamientos:
– Testigo (sin insecticida);
– Dilución al 3,5% aplicada por inmersión;
– Dilución al 3,5% aplicada por riego;
– Dilución al 7% aplicada por inmersión;
– Dilución al 7% aplicada por riego.
Luego de realizar la conducción y la poda de
los brotes axilares de las plantas, se liberaron en
el interior del invernáculo aproximadamente 100
ejemplares de T. absoluta (adultos y pupas), tapan-
Efecto del imidacloprid en el control de la polilla del tomate (Tuta absoluta Meyrick)
do con tul y papel todos las aberturas por donde
pudieran escapar las polillas.
Para evaluar el daño se realizó el cálculo del
porcentaje de folíolos dañados por planta y el
número de lesiones por hoja, a los 27, 34, 41 y 48
días desde la aplicación del producto.
Se implementó un diseño estadístico factorial con
un tratamiento adicional, completamente aleatorio
y con nueve repeticiones por tratamiento; luego los
datos fueron analizados por medio de análisis de
variancia –ANOVA– al 5 y 1 %.
67
RESULTADOS Y DISCUSIÓN
Como consecuencia de la aplicación del imidacloprid se advierte, en primera instancia, que las
plantas tratadas no sufren el ataque de la polilla, o lo
sufren en menor medida que aquellas a las cuales
no se les aplicó dicho insecticida.
A continuación se presentan los datos generados
en las observaciones semanales realizadas.
Como puede observarse en la Figura 1, el porcentaje de folíolos dañados por planta se incrementa
Tabla 1
Promedios registrados a 27 días de la aplicación
Testigo
3,5% riego
3,5% inmersión
7% riego
7% inmersión
Porcentaje de folíolos dañados
por planta
34,88
4,13
16,48
0,00
2,89
Número de lesiones por hoja
3,95
0,49
2,25
0,00
0,24
Tabla 2
Testigo
3,5% riego
3,5% inmersión
7% riego
7% inmersión
por planta
44,60
10,44
26,75
3,20
11,26
8,09
1,50
5,08
0,36
2,38
Tabla 3
Testigo
3,5% riego
3,5% inmersión
7% riego
7% inmersión
por planta
55,47
29,66
45,00
10,40
26,33
11,44
4,81
9,81
1,37
5,74
Tabla 4
Testigo
3,5% riego
3,5% inmersión
7% riego
7% inmersión
por planta
63,48
31,01
48,43
13,47
28,68
14,28
6,75
12,71
1,95
7,48
68
70
60
50
40
30
20
10
0
27 días
34 días
41 días
48 días
Días desde la aplicación
Testigo
3,5% riego
3,5% inmersión
7% riego
7% inmersión
Figura 1. Evolución del daño.
a lo largo del tiempo. Los distintos tratamientos se
diferencian del testigo en mayor o menor medida
y en todos ellos se evidencia un daño de menor
magnitud que en éste.
En la Figura 2 se observa que a los 34 días
de la aplicación hay 3 tratamientos con daños
que permanecen por debajo del umbral de daño
económico (UDE) sugerido por Ariso (1997),
quien considera que para realizar una aplicación
de insecticida en tomate cultivado en invernáculo
se deben observar en promedio 3 lesiones por hoja.
Así, en este ensayo (Figura 2) los tratamientos
realizados alcanzaron este umbral de daño en distintos períodos desde la aplicación: el testigo en la
primera observación (27 días) ya había superado
el umbral mencionado; en los tratamientos 3,5%
inmersión, 7% inmersión, 3,5% riego alcanza el
mismo a los 28, 35 y 37 días, respectivamente,
mientras que el tratamiento 7% riego no alcanzó
este UDE; sin embargo, en este último tratamiento,
no se puede considerar que fue un largo período
de protección de las plantas, ya que se produjo
fitotoxicidad en el tomate.
Con análisis estadístico se verificó la existencia
de diferencias altamente significativas entre ambas
diluciones y también entre las dos formas de aplicación (riego e inmersión) tanto para los resultados de
lesiones por hoja (Tablas 5 a 8) como para porcentaje
de folíolos dañados (Tablas 9 a 12).
No existe interacción AB; Diferencias altamente
significativas entre diluciones; Diferencias altamente
significativas entre aplicaciones.
La dilución al 7% aplicada por riego se descartó
del análisis por haber producido en todas las plantas
Tabla 5
ANOVA. Lesiones por hoja a los 27 días de la aplicación.
Fuentes de
Variación
GL
CM
137.181
2
68.591
Aplicación
9.019
1
Interacción AB
5.266
1
Error
79.394
49
1.620
Total
230.861
53
4.356
Dilución
SC
F
F 0.05
F 0,01
42.332 **
3.185
5.070
9.019
5.567 *
4.035
7.180
5.266
3.250
4.035
7.180
No existe interacción AB; Diferencias altamente significativas entre diluciones; Diferencias significativas entre aplicaciones.
69
15
Lesiones por hoja
12
9
6
3
0
27 días
34 días
41 días
48 días
Días desde la aplicación
Testigo
3,5% riego
7% riego
3,5% inmersión
7% inmersión
Figura 2. Lesiones por hoja a través del tiempo.
Tabla 6
ANOVA. Lesiones por hoja a los 34 días de la aplicación
Fuentes de
Variación
Dilución
Aplicación
Interacción AB
SC
GL
CM
F
431.402
2
215.701
50.353 **
3.185
5.070
70.492
1
70.492
16.456 **
4.035
7.180
4.035
7.180
5.397
1
5.397
Error
209.904
49
4.284
Total
717.195
53
13.532
1.260
F 0,05
F 0,01
No existe interacción AB; Diferencias altamente significativas entre diluciones; Diferencias altamente significativas entre
aplicaciones.
Tabla 7
Fuentes de
Variación
SC
GL
CM
F
F 0,05
F 0,01
Dilución
559.424
2
279.712
51.202 **
3.185
5.070
Aplicación
197.589
1
197.589
36.169 **
4.035
7.180
0.902
1
0.902
4.035
7.180
Error
267.681
49
5.463
Total
1025.597
53
19.351
Interacción AB
0.165
aplicaciones.
70
Tabla 8
Fuentes de
Variación
SC
GL
CM
F
F 0,05
F 0,01
Dilución
824.602
2
412.301
21.110 **
3.185
5.070
Aplicación
297.374
1
297.374
15.225 **
4.035
7.180
0.421
1
0.421
4.035
7.180
Error
957.043
49
19.531
Total
2079.440
53
39.235
Interacción AB
0.022
aplicaciones.
Tabla 9
ANOVA. Porcentaje de folíolos dañados a los 27 días de la aplicación
Fuentes de
Variación
GL
CM
F
F 0,05
F 0,01
10789.821
2
5394.911
28.533 **
3.185
5.070
Aplicación
529.786
1
529.786
2.802
4.035
7.180
Interacción AB
205.504
1
205.504
1.087
4.035
7.180
Error
9264.782
49
189.077
Total
20789.893
53
392.262
Dilución
SC
No existe interacción AB; Diferencias altamente significativas entre diluciones; No hay diferencias entre aplicaciones.
Tabla 10
Fuentes de
Variación
SC
GL
CM
F
13211.075
2
6605.537
36.066 **
3.185
5.070
1337.561
1
1337.561
7.303 **
4.035
7.180
153.031
1
153.031
0.836
4.035
7.180
Error
8974.321
49
183.149
Total
23675.986
53
446.717
Dilución
Aplicación
Interacción AB
F 0,05
F 0,01
aplicaciones.
71
Tabla 11
ANOVA Porcentaje de folíolos dañados a los 41 días de la aplicación
Fuentes de
Variación
Dilución
SC
GL
CM
F
F 0,05
F 0,01
12391.490
2
6195.745
35.632 **
3.185
5.070
2199.270
1
2199.270
12.648 **
4.035
7.180
0.811
1
0.811
4.035
7.180
Error
3520.291
49
173.883
Total
2311.862
53
436.073
Aplicación
Interacción AB
0.005
Tabla 12
Fuentes de
Variación
SC
GL
CM
F
F 0,05
F 0,01
16266.865
2
8133.433
49.073 **
3.185
5.070
2396.430
1
2396.430
14.459 **
4.035
7.180
11.001
1
11.001
4.035
7.180
Error
8121.290
49
165.741
Total
26795.586
53
505.577
Dilución
Aplicación
Interacción AB
0.066
aplicaciones.
tratadas una marcada disminución del crecimiento
y pérdida de hojas.
Los tratamientos que mejor controlaron a la
plaga fueron (figura 1):
– Dilución al 3,5 % aplicada por riego.
– Dilución al 7% aplicada por inmersión.
Como se aprecia en la Figura 2, la aplicación por
inmersión de la dilución al 7% presentó niveles de
daño inferiores al UDE hasta los 37 días después del
tratamiento y la aplicación por riego de la dilución
al 3% hasta los 35 días.
A través de un ensayo, bajo condiciones de
invernáculo, no se puede establecer con certeza
cuál es el tratamiento adecuado para controlar la
polilla del tomate en condiciones de campo, ya que
los resultados tienen sustento sólo en este ámbito
de producción.
Finalmente, en cultivos protegidos de tomate,
teniendo en cuenta aspectos económicos del control de plagas, sería recomendable la aplicación de
imidacloprid a la raíz de las plantas jóvenes por
inmersión (al 7% en agua) durante el transplante,
ya que es el tratamiento que requiere en total una
menor cantidad de producto y tiene una alta eficacia
de control.
CONCLUSIONES
En condiciones de invernáculo la aplicación de
la dilución al 7% aplicada mediante riego resultó
fitotóxica para el tomate platense común.
Las aplicaciones de la dilución al 3,5% aplicada por riego y de la dilución al 7% aplicada por
inmersión resultaron ser las más adecuadas para el
control de la plaga, por su eficacia y periodo posttratamiento con daños menores al UDE.
72
LITERATURA CITADA
ARISO, E. (1997). Comunicación personal, Departamento
Técnico de Bayer.
BETANCOURT, C. M. y SCATONI I. B. (1995). Description
of the development stages of the “tomato borer”,
Scrobipalpuloides absoluta (Mayrick) (Lep., Gelechiidae).
Boletín de investigación, Facultad de Agronomía, Universidad
de la República. 1995, 45: 1-14. Uruguay.
CASAFE (Cámara de Sanidad Agropecuaria y Fertilizantes).
(2001). Guía de productos fitosanitarios para la República
Argentina.1368 pp. CASAFE, Buenos Aires, Argentina.
EPPERLEIN, K.; SCHMIDT, H. W.; SCHWALBE, R. 1997.
Influence of Gaucho R used as seed treatment of maize on
the infestation with viruses, pests and on the epedaphic soil
fauna. Archives of the Phytopatology and Plant Protection,
31 (2): 185-200. Germany.
INTA Centro Regional Cuyo (1991). “Manual de cultivo de
tomate”. INTA, Argentina.
LARRAÍN, P. (1986). Eficacia de insecticidas y frecuencia
de aplicación en S. absoluta. Avicultura Técnica Nº 46,
Chile.
LIMA, J. O. G. de; MACHADO, W. A. 1996. Greenhouse
evaluation of insecticides for control of the tomato leafminer
Scrobipalpuloides absoluta (Meyrick). Revista Ceres. 48
(248): 337-345, Brazil.
REIS, P. R.; SOUZA, J. C. de; DE SOUZA, J. C. 1998. Chemical
control of Tuta absoluta (Meyrick) in staked tomato plants.
Ciencia e Agrotecnologia, 22 (1): 13-21. Brazil.
RIPA, R. (1981). “Avances en el control de la polilla del tomate”.
Agricultura Técnica Nº 41, Chile.

Resistance of Tuta absoluta to insecticides Because

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