Simulium (Nevermannia) itwariense, Krüger, Andreas, 2016

Krüger, Andreas, 2016, The Simulium nigritarse subgroup (Diptera: Simuliidae) in Uganda: New species and country records, Zootaxa 4121 (1), pp. 59-67 : 65-66

Simulium (Nevermannia) itwariense sp. nov.

( Figs. 1 C, 3D, 5A–C)

Medium-sized species, wing length about 3.0 mm.

Female. General habitus darker than in the two species described above. Setae of scutellum and abdomen and scales of mesonotum shiny golden. Postnotum is bare. Setae of wing tufts and basicosta blackish. Colour patterns of the legs as typical for S. nigritarse s.l. Tarsal claws with a large basal tooth. Sensory vesicle (Lutz’s organ) very broad and voluminous, two thirds of the length of the third palpal segment ( Fig. 1 C).

Male. Similar to females except of sexual differences. Dark appearance with shiny golden setae and scales. Setae of wing tufts and basicosta dark. Hind femur dark as in S. perforatum . Basal third of hind tibia yellow. Hind basitarsus dilated, length to width ratio 3.5–3.89 (mean 3.68, n=4). Terminalia of the general S. nigritarse s. l. type, with two pairs of strongly unequal parameral hooks, and the style distinctly shorter than the coxite.

Pupa. Cocoon ( Fig. 5 A) very similar to that in S. bwambanum sp. nov. Anterior rim reinforced, margin medially not, or only slightly produced. In contrast to the two species described above, all four gill filaments arise directly from the basal trunk and remain parallel without angulation or spreading ( Fig. 3 D). The basal trunk ( Fig. 5 B,C) is much longer than wide (300–390 µm), but slightly shorter than in S. nyanzense Fain & Dujardin. The basal vesicle corresponds to type 2. The filament walls are intermediate between types 1 and 2 (see Fig. 2 B), thus differing from S. nyanzense . There are six normal setae on the pilous plate with lengths between 50 µm and more than 100 µm.

Larva. Unknown.

Specimens examined. Holotype: Female emerged from pupa, with pupal case, Kabarole district, Nyakabale river near confl. Wamise, 1460 m, 0°46´38´´N 30°26´20´´E, 10.v.1993, leg. R. Garms. Paratypes (all emerged from pupae): 3 ♀, 3 Ƌ, pupal gills of one female and one male, and hypopygia of two males permanently mounted, same data as holotype.

Other material (all emerged from pupae): 5 ♀, 5 Ƌ, same data as holotype.

Distribution. The sample from the Itwara forest reserve in western Uganda is the only record so far. The Nyakabale is one of several small streams draining from the forest, where only very few simuliid species are to be found. Since the location is not far from river Kamotonga, an occasional sympatry with S. perforatum (see above) is possible. The morphologically very similar and probably closest related species S. nyanzense occurs in Kenya ( Fain & Dujardin, 1983).

Ecological details. The width of Nyakabale measured 2 metres, the stream was fast flowing, covered by vegetation, i.e. thickets of low bush. The water temperature was 19°C, pH 7.0, electrical conductivity 72 µS/cm and total hardness 0.23 mmol/l of alkaline earth ions.

Taxonomic position and recognition. Following the key given by Fain & Dujardin (1983), S. itwariense is closely related to S. nyanzense . In the pupal stage it differs from S. nyanzense by the slightly shorter basal trunk and the irregularly raised structures of the filament walls, which are described to be very short in S. nyanzense . Concerning the adults, the female sensory vesicle resembles those of S. nyanzense , S. sirimonense as well as further species with a broad vesicle.

Etymology. This new species is named after the Itwara forest reserve from where the sample was collected. The area is located some 30 km northeast of Fort Portal in western Uganda.

Keys to the species of S. nigritarse s. l. in Uganda, including the extra-Ugandan species S. nigritarse sensu stricto and S. aureosimile (modified from Fain & Dujardin 1983):

Figures

FIGURE 1. Sensory vesicle (Lutz’s organ) in the 3 rd palpal segment of females. A— Simulium bwambanum sp. nov.; B— S. perforatum; C— S. itwariense sp. nov. Scale bar: A – C = 0.02 mm.

FIGURE 2. Simulium bwambanum sp. nov., pupa. A—cocoon with pupal case, lateral view; B—gill filament wall structure type 1 / 2, below view of surface, above longitudinal view; C—basal trunk of gill. BV—basal vesicle. Scale bar: C = 0.1 mm.

FIGURE 3. Basal aspects of pupal gills. A, B— Simulium bwambanum sp. nov.; C— S. perforatum; D— S. itwariense sp. nov. Scale bar: A – D = 0.5 mm. BV—basal vesicle; PP—pilous plate (approximate location).

FIGURE 5. Simulium itwariense sp. nov., pupa. A—cocoon with pupal case, dorsal view; B, C—basal trunks of gill. Scale bar: B, C = 0.3 mm.