Simulium cerradense, Coscaron, Cerqueira, Sato & La Salvia, 1992, Coscaron, Cerqueira, Sato & La Salvia, 1992

Hamada, Neusa, Luz, Sérgio Luiz Bessa & Coscarón, Sixto, 2004, New morphological information on Simulium cerradense adults and new records of black fly species (Diptera: Simuliidae) in the western region of Bahia state, Brazil, Zootaxa 693 (1), pp. 1-8 : 3-7

Information below on S. cerradense females and males modify the original description of this species which Coscarón et al (1992) based on pharate specimens.

Female. Wing mean length 1.87 mm (n = 4). Scutum black, with posterior illumination, with silver coloration over most of its area and black spots on the central and lateral regions ( Fig. 1 ). With anterior illumination 1+1 central silver stripes, separated by a thin black region and 1+1 lateral silver stripes, separated from the central silver bands by a black region ( Fig. 2 ). In antero­dorsal view ( Fig. 3 ), 1+1 central silver stripes become thinner in the anterior region and become fused; 1+1 lateral silver stripes end, anteriorly, where 1+1 central stripes become fused. The whole body, in dorsal view ( Fig. 4 ), with dorsal illumination, with scutum silver, with four black stripes, the 1+1 central stripes, wider at the posterior end. In the original description ( Coscarón et al. 1992) only the lateral pair of silver bands was represented in the drawing, and this was represented as being thinner than it is. Pleural region black, with silver pruinosity. Abdomen as described in the original description, with tergite II, with certain illumination with 1+1 silver spots. Cephalic characters, legs and genitalia as in original description.

Male: Wing length 1.73 mm (n = 1). Scutum black, with anterior illumination with 1+1 anterior subtriangular silver spots ( Figs 5 and 7 ). With posterior illumination, 1+1 anterior subtriangular silver spots turn dark ( Fig. 6 ), in antero­dorsal view ( Fig. 7 ), silver spots turn black and small, located in a wide anterior silver band that reaches the lateral silver border. Head, legs and genitalia characters as in the original description.

Pupa and larva: Pupal cocoon is thick and dense, with anterior region elevated ( Fig. 9 ), very similar in texture and shape to the cocoon of Simulium lutzianum Pinto. Larval subesophageal ganglion is not pigmented. Pupae and larva as in the original description.

Comments: A black colored scutum with silver bands is a common pattern in Simuliidae , especially in species in the S. ( Psaroniocompsa ); and can also be found in some species of S. ( Psilopelmia ), S. ( Chirostilbia ) and S. ( Aspathia ). In S. ( Psaroniocompsa ) this pattern is common in the S. amazonicum group and in the S. quadrifidum group (sensu Crosskey & Howard 1997) = S. ( Cerqueirellum ) and S. (Coscaroniellum), respectively ( Py­Daniel 1983; Coscarón 1987). This color pattern can vary according to the angle of light incidence on the specimen; species in the first group that show this pattern are S. amazonicum Goeldi , S. argentiscutum Shelley & Luna Dias , S. cuneatum (Enderlein) , S. ganalesense Vargas, Martínez Palacios & Díaz Nájera , S. minusculum Lutz , S. oyapockense Floch & Abonnenc , S. roraimense Nunes de Mello , S. chaquense Coscarón , S. sanguineum Knab and in the second group, S. cerradense and S. quadrifidum Lutz.

A black scutum with paired silver band, with frontal iridescent silver pruinosity and similar female genitalia makes the taxonomic placement of these species difficult. However, other characters permit this species to be separated from those in the amazonicum group, such as frons wider than high, with infra­frontal sutures, female antennae relatively longer than male, cibarium with frontal sclerotised area wider and 1+1 blunt elevations at sides of invaginated median area, fronto­ocular triangle more developed. Absence in scutum of 1+1 elongated, dark spots on silvery vittae bands. Claw with basal tooth; spermatheca proportionately wide; male gonostyle as long as the gonocoxyte and elongated subtriangular shape; pupa gill notably longer than cocoon length; larva integument relatively long with multibranched trichomes; median antennal article relatively shorter in comparison to proximal and distal articles; mandibles without supramarginal setae and presence of 1­2 latero mandibular process; anal sclerite with ventral branches relatively short.

The scutum black with submedian silvery bands reaching the posterior grayish area is present in some species of S. ( Chirostilbia ), S. ( Psilopelmia ) and S. ( Aspathia ), but differences in female cibarium, paraproct and gonostyle are sufficient to separate the species in the quadrifidum group from the other taxa mentioned.

Material examined. Brazil, Bahia state, Luís Eduardo Magalhães County, stream near Roda Velha, Highway BR20 (12 o 29S 45 o 53W). 4/vii/2003: 1M (male) pinned with respective pupal pelt in glycerin (INPA), 5 pupae and 5 larvae in alcohol (INPA); 2M and 2F (female) with respective pupal pelt in alcohol ( Museo de La Plata ). 4/viii/2003: 1M and 4F pinned with respective pupal pelt in glycerin (INPA), 5 pupae and 5 larvae in alcohol (INPA). 2/vii/2004: 5M and 8F pinned with respective pupal pelt in glycerin (INPA), 5 pupae and 5 larvae in alcohol (INPA).

Other black fly species

The black fly species known from Bahia state are: S. perflavum Roubaud , S. inaequale Paterson & Shannon , S. limbatum, Knab , S. subpallidum Lutz , S. brachycladum Lutz & Pinto , S. rubrithorax Lutz , S. subnigrum Lutz , S. spinibranchium Lutz , S. hirtipupa Lutz , S. papaveroi Coscarón , S. incrustatum Lutz , S. cerradense , S. argentiscutum and S. minusculum ( Coscarón 1987; Coscarón et al. 1992; Shelley & Luna Dias 1980). The collected species and their distribution in the surveyed area are listed in Table 1 ; the new black fly occurrences in Bahia state are Simulium exiguum Roubaud and Simulium auripellitum Enderlein. Two unidentified species in the subgenus Psaroniocompsa were also collected; further studies will be necessary to determine their taxonomic identity.

Bionomics

Simulium cerradense was collected only in one stream in the surveyed area; this stream was around three meters in width, one meter in depth, had a sandy bottom and clear, transparent water. The original vegetation in the study area was savanna, but this has largely been replaced by cotton and soybean agriculture. Only part of the stream bank had riparian vegetation. Although this stream crossed the highway it did not show signs of sedimentation; the water was clear with greenish coloration. Larvae and pupae were collected in higher abundance in the area of the stream with the lowest water velocity, usually at the edge of the stream, using macrophyte leaves as substrate. Water temperature was 22 oC, pH 4.9 and conductivity below 10 S/cm. Two black fly species collected with S. cerradense in the sampled stream were: S. perflavum (the most abundant species) and S. ( Psaroniocompsa ) sp.1 (lower abundance).

Figures

FIGURE 9. Pupa of Simulium cerradense (Diptera: Simuliidae), dorsal view.

FIGURES 1–4. Female of Simulium cerradense (Diptera: Simuliidae). 12, Scutum, dorsal view: 1, posterior illumination; 2, anterior illumination. 3, Scutum, antero­dorsal view. 4, dorsal view (posterior illumination).

FIGURES 5–7. Male scutum of Simulium cerradense (Diptera: Simuliidae). 5­6, dorsal view: 5. anterior illumination; 6, posterior illumination. 7. latero­dorsal view; 8, antero­dorsal view.