Simulium cuasiexiguum, a New Blackfly Species (Diptera: Simuliidae) from the Minaçu Area in the State of Goiás, Central Brazil

As part of a long term project on the dispersal of human onchocerciasis from its Amazonia focus to other, non-endemic parts of Brazil prospection for simuliids has been continuing in an effort to obtain representative samples of species from different areas of the country. Intensive collection in the Planalto highland region of central Brazil where human onchocerciasis has been detected at Minaçu in northern of the State of Goiás (MaiaHerzog et al. 1999) several hundred kilometres north of Brasília, has revealed the presence of a new species that is described here. Its importance lies in its similarity to S. exiguum, a vector of human onchocerciasis in Ecuador and Venezuela (Shelley 1988) and a possible vector in the Amazônia focus in northern Brazil (Shelley et al. 1997). Both species are also present at Minaçu.

As part of a long term project on the dispersal of human onchocerciasis from its Amazonia focus to other, non-endemic parts of Brazil prospection for simuliids has been continuing in an effort to obtain representative samples of species from different areas of the country. Intensive collection in the Planalto highland region of central Brazil where human onchocerciasis has been detected at Minaçu in northern of the State of Goiás (Maia-Herzog et al. 1999) several hundred kilometres north of Brasília, has revealed the presence of a new species that is described here. Its importance lies in its similarity to S. exiguum, a vector of human onchocerciasis in Ecuador and Venezuela (Shelley 1988) and a possible vector in the Amazônia focus in northern Brazil . Both species are also present at Minaçu.

MATERIALS AND METHODS
Field collection and specimen preservation and examination methods were those detailed in Shelley et al. (1997) for the simuliid fauna of the Brazilian Amazônia focus of onchocerciasis. Type specimens have been deposited in the Entomology Departments of the British Museum (Natural History) and Oswaldo Cruz Institute as indicated in Material Examined. A "synoptics" image analysis system was used for the production of all the figures of simuliid morphology where a light microscope was used. In the two colour plates only Figs 3,4,6,11 and 12 reflect true colours, the other figures in these plates having been affected by the mountant in the slide preparations. Images have been stored on CD discs and deposited in the above named institutions.  (Fig. 1). Frons, clypeus and occiput black with silver pruinosity. Mouthparts orange-brown. Antennae dark brown with scape, pedicel and first flagellomere orange-brown. Cibarium unarmed (Fig. 2).

Simulium
Scutum and humeri (Fig. 3) greyish black with faint silver pruinosity; one median and a pair of submedian, darker black lines running along whole length of scutum and diverging posteriorly (best seen in females devoid of setae with illumination perpendicular to specimen); scutum with small velvet-black spot adjoining paranotal folds (= paratergites). Paranotal folds black with silvery grey pruinosity. Scutum with numerous, short, recumbent dark setae and discrete groups of short, flattened, brass-coloured setae with greenish reflections. Pleural region silvery grey, pruinose. Scutellum greyish black, faintly pruinose, vestiture of golden setae longer than those on scutum and single row of black bristles on posterior margin.
Subcostal wing vein and basal sector of Radius bare. Costal base tuft of dark hairs.
Head holoptic with dark red eyes; lower, smaller facets with greenish reflections. Clypeus black with silver pruinosity, other head coloration as in female.
Scutum and humeri velvet-black with posterior margin faintly silver pruinose (best seen when specimen tilted) (Fig. 11). Paranotal folds velvetblack with silvery grey pruinosity. Scutum covered in numerous, short, recumbent, light brown setae interspersed amongst groups of brilliant gold, wide setae. Coloration and setation of pleural region, scutellum and postnotum as in female except wide setae on scutellum brilliant gold.
Wing venation, leg coloration and halter coloration as in female.
Abdominal tergites velvet-black, basal fringe dark brown with few long hairs. Silver ornamentation as follows: tergites II and VI all silver except sometimes in median area on VI; tergite VII silver on lateral margins, some specimens with 1+1 lateral silver pruinose patches on posterior margin of tergite VIII; tergite IX shiny black (Fig. 12). Sternites grey with well-developed velvet-black sternal plates on segments II-VIII. Genitalia brownish black. Gonocoxite sub-rectangular; gonostyle small, square, with small, blunt spine on distal inner corner (Figs 13,14). Ventral plate quadrangular with well developed basal arms and pointed apex, small keel, hairs short, diffuse and mainly occurring around median keel (Fig. 15). Median sclerite not seen. Paramere with several apical spines (Fig. 16). Cocoon slipper-shaped, mid to dark brown; rim of aperture dark brown, reinforced and without central protuberance. Cocoon composed of elastic, amorphous substance interwoven with fibres. Gill light brown with six forwardly directed, slender filaments arranged in the vertical plane (Fig. 17), main trunk immediately giving rise to three primary branches each with a single bifurcation in basal tenth of gill. Filaments slender, rounded distally, surfaces covered in fine spicules and prominent transverse ridges. Head (frontoclypeus) with 2+2 poorly developed, simple frontal trichomes and with 1+1 poorly developed, simple facial trichomes; surface of head covered with tubercles (platelets). Thorax with 5+5 antero-dorsal, welldeveloped trichomes of 1-4 branches. Surface of thorax covered with platelets, which are more densely distributed on anterior half. Abdominal tergite II with 4+4 simple hairs in line on posterior border, III-IV with 4+4 simple hooks, VI-VII with patches of poorly developed spine combs on antero-lateral margins, VII and IX with well developed spine combs on anterior border except for central area, IX with 1+1 strong, unbranched spines; sternite IV with 1+1 simple hairs, V with 2+2 bifid or trifid hooks, VI and VII with 2+2 hooks, inner pairs being bifid or trifid and outer pairs simple; sternites IV-VIII with 1+1 patches of poorly developed spine combs on postero-lateral borders.

TAXONOMIC DISCUSSION
S. cuasiexiguum is within the subgenus Notolepria, together with eight other Neotropical species, S. blantoni, S. exiguum, S. gonzalezi, S. incertum, S. llutense, S. paraguayense, S. paranense, S. subexiguum and Simulium sp. A. Ibañez Bernal (Crosskey & Howard 1997). The most important member of this subgenus is S. exiguum because of its wide distribution, common occurrence and anthropophilic habits in some areas, especially where it is a vector of human onchocerciasis. The morphological separation of S. exiguum Roubaud from its closest relatives S. gonzalezi Vargas & Díaz Nájera and S. paraguayense Schrottky has been based by various authors on a combination of characters: form of the female paraproct, genital fork and leg coloration, form of the male genitalia and number of pupal gill filaments and trichome branches. Variations in these characters to the extent of an overlap between species have meant that species identifi-cation from some localities is often not possible without recourse to morphological and cytological examination of large samples of single populations and this has been fully discussed in Shelley et al. (1989Shelley et al. ( , 1997. Subsequent collections in Brazil have revealed a wider distribution of S. exiguum than previously reported and the presence of this new species S. cuasiexiguum, distinct from it in the female, male and pupa. The morphological distinctness of these two species in several areas where they are sympatric shows S. cuasiexiguum to be a good species.
The following morphological comparison (Table)  Simulium cuasiexiguum male and pupa. Fig. 11: scutum. Fig. 12: abdomen. Fig. 13: gonocoxite and gonostyle. Fig. 14: distal part of gonostyle. Fig. 15: ventral plate (ventral view). Fig. 16: parameres. Fig. 17: pupal gill gonzalezi and S. paraguayense is based on large series of reared and biting specimens largely from South America and held in the BMNH and IOC and cited in Material Examined. Comparisons with S. paraguayense are based on the literature (Wygodzinsky 1953, Coscarón & Wygodzinsky 1975. Other variations in characters between S. gonzalezi and S. exiguum from Central America and noted by various authors are not included because they have been based on few specimens (see Shelley et al. 1989Shelley et al. , 1997 and are left to a future analysis integrating various taxonomic techniques. In both sexes leg coloration is variable within species but S. gonzalezi has more extensive dark areas in the legs than the other species and S. paraguayense is the only species with the distal tip of the hind leg basitarsus dark (Table, Figs [18][19][20][21]. In the female the paraprocts of S. cuasiexiguum (Fig. 22) and S. paraguayense (Fig. 28) are long and thin and thereby distinct from typical S. exiguum from Brazil, Ecuador and Venezuela (Figs 23, 24, 26) (although note Fig. 25 of a specimen from Ecuador) and S. gonzalezi (Fig. 27). The genital fork of S. gonzalezi (Fig. 33) is distinct from the other species (Figs 29-32, 34) in its long and thin lateral arms. In the male the gonostyle is square in both S. cuasiexiguum (Fig. 35) and S. paraguayense (Fig. 38) whereas it is triangular in the other two species (Figs 36, 37). Development of the keel and basal arms of the ventral plate also differs between the four species (Figs 39-44) with the greatest development in both S. cuasiexiguum (Fig. 39) and S. paraguayense (Fig. 44). The development of the basal arms is not necessarily a totally reliable character in this case since damage could have occurred to these parts during separation from the rest of the male genitalia, thus giving the appearance of weak development in some cases. Median sclerites are Y shaped in species where this character has been observed and differences occur in overall size and size of the distal incision (Figs 40-42). In S. paraguayense (Wygodzinsky, 1953) the median sclerite is not clearly figured. The number of gill S. cuasiexiguum has a very limited distribution in the Planalto region of Brazil in northern Goiás and in the Mato Grosso (Material Examined;Figs 49,50). It occurs in low numbers on submerged vegetation in small to medium size (10-100 m), fast flowing rivers in the grasslands and gallery forests of the cerrado (savanna) (Material Examined). A comparison of the distributions of both S. cuasiexiguum and S. exiguum was made in relation to vegetation and altitude in Brazil. S. exiguum is largely confined to forest and cerrado areas in the more highland regions of Roraima and the central Planalto of Goiás states, whereas S. cuasiexiguum is a cerrado species in a discrete area of high altitude in central Brazil (Figs 49, 50). S. cuasiexiguum is apparently zoophilic while both zoophilic and anthropophilic populations of S. exiguum in the Neotropical region are widespread and dealt with in Shelley et al. (1997). S. gonzalezi has only been recorded from Belize, Ecuador, Guatemala and Mexico. S. paraguayense occurs in Paraguay, northern Argentina and southern Brazil but some of the earlier records are in doubt because of possible species misidentification (Coscarón 1991).

MATERIAL EXAMINED
The following abbreviations are used for deposi-   (BMNH).