Spatial Distribution of Black Fly (Diptera: Simuliidae) Immatures in a

Spatial Distribution of Black Fly (Diptera: Simuliidae) Immatures in a Water
Current Velocity Gradient in Aracruz/ES, Brazil
Karina Bertazo1
Ronaldo Figueiró 2,3
RESUMO
Distribuição espacial de imaturos de simulídeos em gradientes de velocidade de correnteza
em Aracruz, ES/Brasil. Este estudo teve como objetivo descrever as associações das larvas a
diferentes velocidades e verificar se os trechos com maior amplitude de variação são mais ricos
e diversos. Para obtenção da amostragem, utilizamos quadrats distribuídos aleatoriamente no
riacho do César. Foram encontradas 15888 larvas e cinco espécies de simulídeos: Simulium
perflavum Roubaud 1906, Simulium subpallidum Lutz 1910, Simulium brachycladum Lutz & Pinto
1932, Simulium (Psaroniocompsa) sp. e Simulium spinibranchium Lutz 1910. S. brachycladum foi a mais
abundante e apresentou associação com velocidades médias. Já S. subpallidum, a segunda mais
abundante, associou-se a diferentes velocidades para cada trecho estudado.
Palavras-chave: ecologia; neotropical; velocidade d’água.
ABSTRACT
Spatial distribution of black fly (Diptera: Simuliidae) immatures in a water current velocity
gradient in Aracruz/ES, Brazil. The aim of this study was to describe black fly larvae
associations with different water current velocities and verify if the sections of the stream
with wider ranges of water velocities were the most species-rich and diverse. Sampling was
done using randomly distributed quadrats along stream sections of the César stream and
15 888 larvae belonging to five black fly species sampled: Simulium perflavum Roubaud 1906,
S. subpallidum Lutz 1910, S. brachycladum Lutz & Pinto 1932, S. (Psaroniocompsa) sp. and S.
spinibranchium Lutz 1910. Of these, S. brachycladum was the most abundant and showed an
1 Universidade Federal do Espírito Santo (UFES)
2 Centro Universitário de Volta Redonda (UniFOA)
3 Centro Universitário Estadual da Zona Oeste (UEZO)
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Spatial Distribution of Black Fly...
association with intermediate current velocities. The second most abundant species, S.
subpallidum, was found associated with different velocities at each sampling site.
Key words: ecology; neotropical; water flow speed.
INTRODUCTION
Black flies are insects that at high densities can be a significant biting nuisance to the human
population and livestock, causing allergic reactions and transmission of diseases (STRIEDER
et al., 1992). Their development occurs in lotic habitats, where their filter-feeding larvae
form part of the diet of fish and of other aquatic insects (COSCARÓN, 1991). Several
environmental factors are associated with species richness and distribution, such as water
current velocity, nature of the substrate and vegetation cover (COSCARÓN et al., 1996;
HAMADA & MCCREADIE, 1999). According to Malmqvist & Sackman (1996), higher
current velocities may reduce predation and create refuges, even at the cost of lower availability
of food. Although the influence of the substrate and vegetation cover has been widely
investigated in the Neotropical region, (GRILLET & BARREIRA, 1997; PEPINELLI et al.,
2005; FIGUEIRÓ et al., 2006), that of current velocity still has not been adequately studied.
Santos Júnior et al. (2007) confirmed that S. pertinax larvae tend to occupy microhabitats
with lower density of predators. Figueiró et al. (2008), studying the distribution of different
species along a velocity gradient, found that the species presented associations with different
ranges of current speed, and proposed that the degree of variation in water might reflects the
heterogeneity of black flies habitats, being directly proportional to diversity. The colonization
of these different microhabitats may be a strategy for coexistence of species (PALMER &
CRAIG, 2000).
Given that few studies on black flies ecology in Brazil have been carried out to date, the
objective of this study was to describe the associations of simuliid larvae with different current
velocities.
MATERIALS AND METHODS
Sampling was carried out in May 2010 in a stream located within the municipality of Aracruz,
in the Brazilian state of Espírito Santo. The stream ran through an area of pasture (coordinates
19º43’39.99”S and 40º14’57.74”W). It had a rocky bed, average depth of the 30 cm and
its width never exceeded 3m. Five 10m-long stream sections were chosen and 15 samples
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BERTAZO, K.; et al.
collected from each of these using 30 x 30cm quadrats, based on the methodology described
in Figueiró et al. (2006). In each sample, taken randomly among the potential breeding sites,
all the immature black flies encountered adhering to rocky substrates were removed and the
mean water velocity measured by means of the head rod method. In this method, a ruler is
placed touching the bottom of the river, with the sharp edge facing upstream, then the depth
is calculated and the ruler is revolved 90 degrees, when the “head”, which is the water elevation
caused by the impingement of the water against the broad edge of the ruler, is annotated and
both are used in the formula suggested by Wilm & Storey (1944). The larvae were separated
by similar morphotypes and identified to species based on the patterns of cephalic patches
through comparison with those having mature branchial histoblasts (COSCARÓN, 1984,
1991). Data on relative abundance of the species was then separated among four current
velocity classes for each stretch of the stream studied (table I). This data were submitted to
correspondence analyses to ordinate the distribution patterns of simuliid larvae among the
classes. (COSCARÓN, 1984, 1991).
Table I: water velocity classes of the stretches and its respective associated species according
to the correspondence analyses.
STRETCH 1
0.44 m.s - 0.57 m.s
-1
-1
Simulium perflavum
Simulium subpallidum
Simulium (Psaroniocompsa) sp.
Simulium brachycladum
S. perflavum
0.58 m.s - 0.71 m.s
-1
-1
S. subpallidum
S. (Psaroniocompsa) sp.
S. brachycladum
S. perflavum
0.72 m.s - 0.85 m.s
-1
-1
S. subpallidum
S. (Psaroniocompsa) sp.
S. brachycladum
0.86 m.s-1 - 0.99 m.s-1
S. perflavum
S. subpallidum
S. brachycladum
STRETCH 2
0.44 m.s - 0.69 m.s
-1
-1
S. perflavum
S. subpallidum
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93
Spatial Distribution of Black Fly...
S. brachycladum
0.70 m. s - 0.94 m.s
-1
-1
S. perflavum
S. subpallidum
S. brachycladum
S. perflavum
0.95 m.s - 1.2 m.s
-1
-1
S. subpallidum
S. brachycladum
S. perflavum
1.21 m.s-1 - 1.46 m.s-1
S. subpallidum
S. brachycladum
STRETCH 3
0.54 m.s - 0.73 m. s
-1
-1
S. perflavum
S. subpallidum
S. brachycladum
0.74 m. s - 0.92 m.s
-1
-1
S. perflavum
S. subpallidum
S. brachycladum
0.93 m. s - 1.11 m.s
-1
-1
S. perflavum
S. subpallidum
S. brachycladum
1.12 m. s - 1.32 m. s
-1
-1
S. perflavum
S. subpallidum
S. brachycladum
STRETCH 4
0.62 m.s-1 - 0.87 m.s-1
S. subpallidum
S. brachycladum
0.88 m. s - 1.12 m. s
-1
-1
S. subpallidum
S. brachycladum
1.13 m.s - 1.37 m.s
-1
-1
S. subpallidum
S. brachycladum
1.38 m.s - 1.65 m.s
-1
-1
S. subpallidum
S. brachycladum
STRETCH 5
0.62 m.s - 0.81 m.s
-1
-1
S. perflavum
S. subpallidum
S. (Psaroniocompsa) sp.
S. brachycladum
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BERTAZO, K.; et al.
Simulium spinibranchium
0.82 m.s - 1.00 m.s
-1
-1
S. perflavum
S. subpallidum
S. brachycladum
S. spinibranchium
1.01 m.s - 1.19 m.s
-1
-1
S. perflavum
S. subpallidum
S. brachycladum
S. spinibranchium
1.20 m.s-1 - 1.40 m.s-1
S. subpallidum
S. brachycladum
S. spinibranchium
RESULTS AND DISCUSSION
Five species of black flies were found in samples from the César stream; Simulium perflavum
Roubaud 1906, Simulium subpallidum Lutz 1910, Simulium brachycladum Lutz & Pinto 1932,
Simulium (Psaroniocompsa) sp. and Simulium spinibranchium Lutz 1910, summing up to 15 888
larvae. The last species was reported in Bertazo et al. (2010) as a new state record for Espírito
Santo.
Among the species found, S. brachycladum was the most abundant with 14 251 specimens
(89.7% of the total), followed by S. subpallidum with 1031 (6.5%), S. perflavum with 434 (2.7%),
S. spinibranchium 113 (0.7%) and S. (Psaroniocompsa) sp. with 59 (0.4%) (Table II).
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Spatial Distribution of Black Fly...
Table II: abundances of black fly larvae in the César stream, Aracruz, Espírito Santo, Brazil.
Stream
section
S.perflavum
S. subpallidum
S. (Psaroniocompsa)sp
S. brachycladum
S. spinibranchium
Larvae
Pupae
Larvae
Pupae
Larvae
Pupae
Larvae
Pupae
Larvae
Pupae
1
409
34
194
41
58
24
354
88
0
0
2
17
6
205
4
0
6
1008
27
0
0
3
5
0
305
0
0
0
2610
6
0
0
4
0
0
147
0
0
0
6097
9
5
0
5
3
0
180
0
1
0
4182
18
108
2
Total
434
40
1031
45
59
30
14251
148
113
2
According to Coscarón (1991) and Shelley et al. (2004), S. brachycladum, S. perflavum and S.
spinibranchium are associated with rocky bed streams, while S. subpallidum is generally found
attached to the riparian vegetation (COSCARÓN, 1991). It is possible that the high density
of S. brachycladum is caused by the fact that the stream offers a great amount of the substrate
type in which this species is commonly found. Shelley et al. (2004) reported that S. perflavum
is often found in small and shallow breeding sites and well insolated places (COSCARÓN,
1991), which are the same conditions of the study area. The study stream has anthropogenic
influence, no canopy cover and is surrounded by pastures.
Larval distribution and species richness varied between all the sampling sections. S. brachycladum
and S. subpallidum immatures were found in all the studied sections, while S. perflavum was not
found only in T4. S. spinibranchium and S. (Pasaroniocompsa) sp were sampled in T4 and T5 and
T1 and T5, respectively. Hence, species richness was S=3 for T2, T3 and T4 and S=4 for T1;
the most diverse section, showing all the five Simuliidae species was T5 (Table III).
Table III: occurrence of black flies in the five sections in the stream Aracruz/Espírito Santo
according to the velocity of water (m.s-1).
S.
Stream section S. brachycladum S. perflavum S. (Psaroniocompsa) sp S. subpallidum spinibranchium
1
0.86 - 0.99
0.58 - 0.71
0.44 - 0.57
0.72 - 0.85
0
2
0.95 - 1.2
0.70 - 0.94
0
1.21 - 1.46
0
3
1.12 - 1.32
0.74 - 0.92
0
0.54 - 0.73
0
4
1.13 - 1.37
0
0
1.38 - 1.65
0.88 - 1.12
5
1.02 - 1.19
0.62 - 0.81
0.62 - 0.81
0.82 - 1.00
1.20 - 1.40
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BERTAZO, K.; et al.
The correspondence analyses pointed a S. brachycladum association with the fastest speed class
in the first and third sections, while in the other there was a trend towards intermediary speeds
(Figure 1). However, even though these flows are classified as intermediary or high, it is possible
to observe that the values often show overlap (for example, the high velocity of T1 is within
the intermediate velocity in T2 and T4). Therefore, we can affirm that this species seems to
respond better to this water current velocity interval. This hypothesis can be corroborated by
Coscarón (1991), which stated that S. brachycladum is associated to intermediate water velocities.
The Simulium perflavum specimens were associated to intermediate velocities, appearing only
in the T5 associated to low velocities (Figure 1). However, just like the previously mentioned
species, the water velocity class in which it is found in T5 is also in the intermediate velocities
class in the other sections where it was found, what lead us to postulate that S. perflavum is
associated to this velocity class.
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Spatial Distribution of Black Fly...
Figure 1: Correspondence analyses for black fly larvae and classes of water current velocity
(m.s-1) in the César stream, Aracruz, Espírito Santo, Brazil.
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BERTAZO, K.; et al.
Hamada & McCreadie (1999) reported that this species has a trend towards small streams,
with good sunlight incidence and slow water current velocities, as well as a trend towards sites
with antropogenic influence (reservoirs). With regard to S. (Psaroniocompsa) sp. this species was
associated with low current velocities in both stream sections where it was sampled, while
S. spinibranchium was associated with more rapid classes of current (Figure 1). Coscarón &
Coscarón-Arias (2007) associated S. spinibranchium with rivers with medium current velocity.
However, S. subpallidum presented different associations with current velocity in each stream
section. In stream sections 1 and 5, this tended to occur at medium velocity, while in stream
sections 2 and 4 it occupied fast-flowing water. In stream section 3 it was found in niches
associated with low velocities of water current (Fig. 1). This species was associated with low
velocity sites by Coscarón (1991) and Figueiró et al. (2008), and high velocities by Pepinelli
(2003) and Coppo & Lopes (2010). This fact reflects the diverse microhabitats colonization
capacity of S. subpallidum. Figueiró et al. (2012) showed that the speed associations of the same
set of black fly species varied among sites, probably reflecting different realized niches due to
different competitive pressure, thus indicating that these associations are a mechanism which
allows local coexistence of such organisms.
Although each species is associated with a class of velocity in each stream section, we found
that S. brachycladum, S. perflavum, S. (Psaroniocompsa) sp. and S. spinibranchium always responded
to the same intervals of water velocity values, while a different behaviour was observed in
S. subpallidum (Table II). This fact leads us to hypothesize that these species show a more
specialized behavior, while S. subpallidum, is more generalist.
Acknowledgements
The authors would like to thank the two anonymous reviewers for the valuable contributions.
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