Cytotaxonomic description ofSimulium kaffaense, a new member of theS. damnosumcomplex (Diptera: Simuliidae) from south–western Ethiopia

Abstract

Although Ethiopia is one of the countries worst affected by human onchocerciasis, the exact taxonomic identity of the blackflies acting as the main vectors in the endemic areas has never been determined. A cytotaxonomic analysis of Simulium damnosum s.l. collected from three endemic sites in south-western Ethiopia has now revealed the existence of the 'Kisiwani' form (a non-anthropophilic cytoform that is common in East Africa) and a newly recognized species, Simulium kaffaense. Simulium kaffaense sp. nov. is differentiated from other members of the S. damnosum complex by six fixed inversions and dozens of 'new' floating inversions. The rearing of egg batches from some of the biting adult females, to larvae or adults, indicated that the human-biting blackflies were all S. kaffaense. As S. kaffaense is not only highly anthropophilic but also, apparently, the only anthropophilic member of the S. damnosum complex present, it is likely to be the main (if not the only) vector of Onchocerca volvulus in the study area. The presence of inversion 1S-1 and a complex inversion possibly involving 1L-3 indicates that S. kaffaense either belongs or is close to the 'Nile' phylogenetic group of S. damnosum s. l. The karyotype frequencies of the inversions in the collections from the three study sites indicate that at least two forms of S. kaffaense, here designated 'Bebeka' and 'Jimma', were caught. The taxonomy and medical importance of S. kaffaense are discussed.

Descriptions of members of theSimulium damnosumcomplex (Diptera: Simuliidae) from southern Africa, Ethiopia and Tanzania

“…cytoform ('Olifants') has been described from north-western South Africa (Krü ger et al, 2005) but this form could not be found among the specimens collected in 1981. The present results confirm the occurrence of two distinct cytoforms in southwestern Ethiopia, which are related to the 'Kisiwani' form (Dunbar and Vajime, 1972) and S. kaffaense (previously known as the 'Jimma' cytoform; Dunbar and Vajime, 1981;Hadis et al, 2005). The results include the first records for Ilubabor province, all previous studies on S. damnosum s.l.…”

“…The distinction made between 'Kisiwani E' and its southern relatives needs confirmation, by the collection and examination of specimens from southern or central Ethiopia. The small sample size and the detection of a newly recognized inversion (2L-207) made it impossible to say whether the S. kaffaense identified in the present study were identical with one of the two cytotypes identified by Hadis et al (2005) or whether they represented another distinct sub-population. The River-Sor specimens appeared to have a higher frequency of inversion 2L-13 (with two homozygotes for this inversion) than the specimens found in the other rivers, and included the only specimen found to have the 3L-8 inversion ( Table 2).…”

“…The results include the first records for Ilubabor province, all previous studies on S. damnosum s.l. in Ethiopia having been carried out near Jima town, in the neighbouring Kaffa province, or in southern Ethiopia, at Arba Minch (Dunbar and Vajime, 1981;Hadis et al, 2005). The distinction made between 'Kisiwani E' and its southern relatives needs confirmation, by the collection and examination of specimens from southern or central Ethiopia.…”

“…Larvae with fixed inversion 1S-1 are here considered to be S. kaffaense (Hadis et al, 2005), and were also characterized by the (Table 2) did not allow these larvae to be clearly assigned to either of the two forms of S. kaffaense described by Hadis et al (2005). Fig.…”

“…Both the 'Kulfo' and 'Kisiwani' forms were recorded from onchocerciasis-free areas in southern Ethiopia but the 'Jimma' form was suspected to be the vector in Kaffa province (Raybould and White, 1979). Hadis et al (2005) recently assigned a new form ('Bebeka') and the 'Jimma' form to a new cytospecies, S. kaffaense, which they believed to be the local vector. In terms of its chromosomes, S. kaffaense is phylogenetically near the 'Nile' group of the complex.…”