Simulium (Nevermannia) bwambanum, 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 : 60-62

Simulium (Nevermannia) bwambanum sp. nov.

( Figs. 1 A, 2A–C, 3A,B)

Medium-sized species, wing length about 3.0 mm.

Female. General habitus as described for S. nigritarse s. l. Setae of scutellum and abdomen pale golden or silvery. Mesonotum brownish with pale golden or silvery scales. Postnotum is bare. Setae of wing tufts and basicosta mainly golden, sometimes with a few dark ones. Colour patterns of the legs as typical for S. nigritarse s. l. Tarsal claws with a large basal tooth. Sensory vesicle (Lutz’s organ) small, distinctly shorter than half of the length of the third palpal segment ( Fig. 1 A).

Male. Similar to females except for sexual differences. Hind femur in the distal half or third dark, the basal part yellowish. Basal half of hind tibia yellow. Hind basitarsus dilated, length to width ratio 3.56–4.25 (mean 3.92, 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 finely woven without perforations ( Fig. 2 A). Anterior rim not, or only slightly reinforced, but not produced. Gill filaments ( Figs. 2 A, 3A,B) almost indistinguishable from those of S. perforatum (see below), resembling the configuration of S. arabicum . The upper pair of filaments arise from a very short common stalk, which is shorter than in S. perforatum and S. arabicum . The other two filaments arise directly from the basal trunk. At least the uppermost and the second filaments are spreading, both of them also suddenly bent downwards. Filament walls ( Fig. 2 B) are considered as intermediate between types 1 and 2 ( Fain & Dujardin, 1983), i.e. with a slightly raised reticulum of obliquely directed lines of short piliform structures. The basal vesicle is well developed and slightly shorter than the basal trunk, i.e. intermediate between types 2 and 3 ( Fig. 2 C, 3A,B). Pilous plate with normal setae.

Larva. Unknown.

Specimens examined. Holotype: ♀ emerged from pupa, with pupal case, Bundibugyo ditrict, Bemara river, 849 m, 0°42´25´´N 30°4´40´´E, 10.viii.1991, leg. R. Garms. Paratypes (all emerged from pupae): 2 ♀, 2 Ƌ, one male of which pupal gills are permanently mounted, same data as holotype; 2 ♀, Kabarole district, Mpanga river at Mitandi road, 1631 m, 0°39´54´´N 30°10´39´´E, 1.viii.1991, leg. R. Garms.

Other material (all emerged from pupae): 6 ♀, 7 Ƌ, same data as holotype; 6 ♀, Kabarole district, Mpanga river at Mitandi road, 1631 m, 0°39´54´´N 30°10´39´´E, 1.viii.1991, leg. R. Garms; 1 Ƌ, same but 2.viii.1991; 2 ♀, Kabarole district, Dunga river at Mitandi road, 1704 m, 0°37´25´´N 30°9´26´´E, 1.viii.1991, leg. R.Garms, 1 Ƌ, Kabarole district, Mahoma river at Mitandi road, 1829 m, 0°36´30´´N 30°8´49´´E, 1.viii.1991, leg. R. Garms.

Distribution. As known from several species of the subgroup, also S. bwambanum sp. nov. seems to be restricted to mountainous habitats. So far, the species is only known from the sites listed above, situated on the northern slopes of the Ruwenzori mountains in western Uganda at altitudes from 850 to 1830 m. All mentioned rivers emerge near the Bwamba pass between the districts Kabarole and Bundibugyo, river Bemara draining to the northwestern, the others to southeastern directions. In all four rivers sympatric with S. perforatum , in rivers Bemara, Mahoma and Mpanga with S. dentulosum Roubaud and in the Bemara also with S. damnosum s. l., S. unicornutum Pomeroy and S. hirsutum Pomeroy. Water temperatures: Bemara 20°C, Dunga 17°C, Mahoma 19°C, Mpanga 16°C.

Taxonomic position and recognition. This new species was recognized in western Uganda in 1991 by R. Garms and tentatively identified as S. aureosimile . Applying the criteria of Fain & Dujardin (1983), the new species differs in most pupal characters from S. aureosimile , showing a mixture of characters of several other species. The most typical features are the configuration of the gill filaments (shared only by S. arabicum , S. perforatum and, partially, S. brachium ), combined with the finely woven cocoon (not in S. perforatum and S. brachium ) and the slightly raised reticulum (not in S. arabicum ). The adults of S. bwambanum sp. nov. differ from those of S. nigritarse s. str. and S. arabicum by the absence of scales on the postnotum, from those of S. perforatum and S. itwariense sp. nov. by the generally paler habitus, including pale setae of wing tufts and basicosta. The latter characters were not described in the revision by Fain & Dujardin (1983) and, therefore, cannot be discussed in comparison with further species of the subgroup.

Etymology. This new species is named after the Bwamba pass which is located in the northern slopes of the Ruwenzori Mountains in western Uganda. Near this place, all rivers emerge from where S. bwambanum sp. nov. was collected.

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.