Simulium (Chirostilbia) brunnescens (diptera: Simuliidae) - new species from the Brazilian cerrado, Manso dam, state of Mato Grosso, Brazil

A new species of Simuliidae, Simulium (Chirostilbia) brunnescens, was discovered at Chapada dos Guimarães, state of Mato Grosso, Brazil, and nearby municipalities (Paranatinga, Rosário do Oeste and Nobres). This species is described here based on the adults, pupae and larvae. This species is closely related to Simulium (C.) subpallidum Lutz, but could be differentiated in all stages: females, leg colour pattern and frontal dilatation size; males, gonostyle shape; pupae, number of gill filaments; larvae, body size and colour, postgenal cleft, ratio between antenna and stalk of labral fan.


MaterialS and MethodS
During field studies of the Simuliidae fauna of the Manso Dam area (MT), carried out by the Laboratório de Simulídeos e Oncocercose, Instituto Oswaldo Cruz-Fundação Oswaldo Cruz (LSO/IOC-Fiocruz), state of Rio de Janeiro, Brazil a new species was found, which is described here.The reservoir has an area of 427 km 2 and spans through the municipalities of Chapada dos Guimarães and Nova Brasilândia, in the Brazilian cerrado, a biodiversity hotspot according to Myers et al. (2000).The climate is tropical (hot and humid, with 4-5 dry months).Annual temperatures average 24ºC and annual rainfall is between 1.250-1.500mm.The area has a plain relief, with steep cliffs and vegetation typical of the savannas (Brazilian cerrado or tropical savanna), with open arboreal semblance.The mean altitude is 810 m (Ross 2003).
During this study, a total of 107 collection sites at the municipalities of Chapada dos Guimarães, Paranatinga, Rosário do Oeste and Nobres were investigated.The width and depth range of the sampled sites was 30-20 m and 10 cm-1 m, respectively, however, most of these sites consisted primarily of low order streams.The region has altitudes ranging from 200-633 m, but mainly from 200-252 m.Sampling of immatures was carried out in 2002 (October) and 2003 (February, April and July).Subsequent collections were made in 2010 (January, April, September and November).The following parameters were measured at each site investigated: water temperature, pH and stream width and depth.On each site, we collected randomly for 15 min by searching immature in all available substrates.Immatures were manually collected, including the substrate whenever possible and placed into tagged clear plastic bags (40 cm x 40 cm) that were put into a cooler with ice and transported to the laboratory.Larvae were fixed in 70% ethanol.Each pupa was placed in an individually tagged microcentrifuge tubes (1.5 mL) with filter paper to remove excessive humidity and also maintain the humidity in order to allow emergence.Adults were either fixed in 70% ethanol or pinned.Slides were prepared according to Calvão-Brito and Maia-Herzog (2003).Pictures were taken using a digital camera (Nikon 995, HP Photosmart M307 and Sony Cybershot H5) connected to a Nikon Eclipse E200, or to a Nikon SMZ800 stereomicroscope or using an Imaging Analyses System (Shelley et al. 2000).
The holotype and paratypes are deposited in the Simulids Collections of IOC (CSIOC).Taxonomic com-IOC (CSIOC).Diagnosis -General colour of adults orange brown.Hypoginial valve unsclerotized, subtriangular.Anal lobe triangular.Cerci membranous, hemispherical.Genital fork and vertical anterior process weakly sclerotized, lateral arms well developed and sclerotized.Spermatheca oval, without ornamentation.Claws without subbasal tooth.Ventral plate trapezoid-shaped with short lateral arms and short hairs apicomedially.Gonocoxite subquadrangular with conic gonostylus.Pupae with slippershaped cocoon, light brown.Gills with six filaments in vertical plane, rising from three short primary branches which bifurcate near base, with rounded end.Larvae with body colour generally dirty white with vivid green markings; dorsal view of the head with 1 + 1 faint posterolateral spots, posteromedial and anteromedial spots continuous in a distinct longitudinal stripe.Antennae with proximal and medial articles unpigmented contrasting with dark distal article; postgenal cleft deep, longer than wide and rounded; abdomen without ventral tubercles.
Female -Medium size of the species (dried specimens, measurement 2 years after collection).Body length: 1.77-2.02mm [mean = 1.89 mm, standard deviation (SD) = 0.086, n = 9] and wing length x width: 1.96-2.08mm (mean = 2 mm, SD = 0.039 mm, n = 9) x 0.89-1.06mm (mean = 0.97 mm, SD = 0.055, n = 9).General colour body in freshly emerged specimens orange brown.Head: eyes green, but dark reddish brown in dried specimens.Frons and clypeus brown with dense silver pruinosity, antenna light brown, mouthparts light brown, maxilla with base of palps dark brown.Frontal dilatation slightly wider at base than at apex, nudiocular area poorly developed (Fig. 38).Palps with segment V equal in length to combined segments III and IV and Lutz sensorial organ well developed, elongated, occupying half of the length of its segment.Lacinia with 18-21 teeth.Mandibles with a row of minute teeth, external Figs 1-10: Simulium brunnescens sp.nov.(Diptera: Simuliidae) female; 1: scutum colour pattern, anterior illumination; 2: posterior illumination; 3: colour pattern of abdomen, green variation; 4: colour pattern of abdomen, brown variation; 5: part of wing; 6: cibarium; 7: hypogynial valve; 8: anal lobe; 9: schematic drawing of genital fork; 10: spermatheca.teeth curved, without space among them.Cibarium unarmed, with sclerotized laterals (Fig. 6).Thorax: scutum orange brown, with golden pilosity, with dark.Some specimens present 1 + 1 dark brown shapes at the bottom of scutum external borders.Humeri and pleural membrane greenish yellow.Katepisternum light brown with pruinosity.Scutellum pale yellow; postnotum dark brown.In both standard illumination positions (anterior and posterior), a lyre-shape pattern can be seen, varying in thickness depending on the position of the light source: brown with anterior illumination (Fig. 1) and yellowish brown with posterior illumination (Fig. 2).Wings: costa with a row of spines between setae, subcosta with four-six small setae, basal section of radius with 12-16 setae, the remaining with approximately 12 spines between setae (Fig. 5).Legs: fore leg (Fig. 30): coxa, trochanter and femur yellow; tibia yellow except for distal part brown.Basitarsus and tarsi dark brown.Claws without subbasal tooth.Mid legs (Fig. 31): coxa yellow, with external face brown; trochanter, femur and tibia yellow; basitarsus and tarsi pale yellow with brown distal part; 3rd and 4th tarsi light brown.Claws without subbasal tooth.Hind legs (Fig. 32): coxa, trochanter and three fourths of femur yellow, the rest dark brown.Proximal three fourths of tibia yellow, gradually fading to dark brown.Four fifths of basitarsus light yellow, brown on distal part; half of 2nd tarsi yellow, the rest of tarsi brown.Calcipala and pedisulcus well devel-oped, calcipala wider than long.Claws with small sub basal tooth.Abdomen: general colour brown, but using the same light source positioning, some colour variation can be seen: some specimens present greenish abdomen (Figs 3,4).Tergites I-II brown, in some specimens bright green, tergites II-V with median velvet brown plates; tergite V median plate more developed, double the width of the other plates.Tergites IV-VII faint brown, greenish in some specimens.Terminalia: hypoginial valve unsclerotized, subtriangular, with around 6 + 6 setae on 8th sternite (Fig. 7).Anal lobe triangular three times as wide as long.Cerci membranous, hemispherical (Fig. 8).Genital fork and vertical anterior process weakly sclerotized, lateral arms well developed and sclerotized (Fig. 9).Spermatheca oval, strongly sclerotized, without ornamentation and microtrichia uniformly arranged throughout the spermatheca, duct junction slightly funnelled, not sclerotized (Fig. 10).
The Simuliidae are a morphologically homogenous group with many recognized species complexes.Some species can only be identified using the configuration of the pupal gill filaments.The subgenus Inaequalium, for example, is known for the extreme similarity among the adults and apparently trivial differences, such as gill bifurcations or the shape of the apex of the gill are used for species identification.We agree with the literature (WHO 1978, Rothfels 1979, Crosskey 1993, Adler & Kachvorian 2001) that cytogenetics and molecular biology are promising methods to solve pending taxonomic problems in this family.Nonetheless, the differences between S. brunnescens and S. subpallidum are solid and constant in the examined populations to be considered a new species.Some articles suggest that the ramification pattern of the pupal gill filaments may not be a reliable source of differentiation in some groups due to its high variability.However, recent descriptions of new species based on both classic taxonomy and molecular tools, prove that morphological characteristics once considered to be variations (presence of small tubercles, differences in ramification), are indeed characters of differentiation, e.g.Hamada et al. (2010) recent description of S. litobranchium vs. Simulium guianense.
Besides the number of pupal gill filaments, some other differences could be found between S. brunnescens and S. subpallidum in the adults -different colour pattern of the legs (the dark spots on the hindfemur and foretibia of S. brunnescens are more conspicuous than the corresponding dots of S. subpallidum), males -the gonostyle is very similar in both species, but it is more slender and pointed in S. brunnescens, ventral plate less rounded than S. subpallidum's, females -the frontal dilatation is broader in S. subpallidum than in S. brunnescens , larvae -in S. brunnescens the coloration is vivid green, while in S. subpallidum is greenish gray size about 4 mm and the postgenal cleft rounded; contrasting if S. subpallidum that the coloration is greenish gray, size about 5 mm and postgular cleft rounded with anterior region narrower.Also, the number of gill filaments on the larval histoblast is different in both species, six in S. brunnescens and eight in S. subpallidum.