African horsesickness epidemiology : five species of Culicoides (Diptera: Ceratopogonidae) collected live behind the ears and at the dung of the African elephant in the Kruger National Park, South Africa

Abstract

During the culling of elephants (Loxodonta africana) at five sites in the Kruger National Park, South Africa, a total of 682 Culicoides of five species of the subgenus Avaritia were found live either behind the ears of elephants or attracted to the freshly disembowelled intestinal dung of elephants. The species are Culicoides tororoensis Khamala & Kettle, 1971; C. kanagai Khamala & Kettle, 1971; C. loxodontis Meiswinkel, 1992, and two undescribed species, i.e. Culicoides sp. #50 and Culicoides sp. #54 pale form (p.f.). Of 511 female midges found behind ears, 39,9% were nulliparous, 57,3% empty parous, 2,5% freshly bloodfed and 0,2% gravid. The age composition of this subpopulation indicates that the Culicoides were behind the ears to suck blood and, furthermore, would do so in broad daylight. The age composition of 171 Culicoides of three species attracted to dung was entirely different: 1,8% nulliparous, 14,6% empty parous, and 83,0% gravid, indicating that the great majority of midges captured at dung were about to oviposit or had just oviposited. Immediately after culling, light-traps were operated at two of the sites. Of 4 023 Culicoides of 21 species captured, 93% were of the same five species found on the ears and at the dung of elephants. Using these and other unpublished data pertaining to the rearing of these five Avaritia species from elephant dung over the past seven years, we broadly sketch the life cycle of these Culicoides, the first for any Afrotropical species of the genus. We also discuss the implications the close association between elephant and midge has for the dispersal and geographic distribution of the latter, and how it may influence the involvement of midges in the transmission of diseases such as African horsesickness. Owing to difficulties in identifying species of the subgenus Avaritia in the Afrotropical Region, the taxonomy of each of the five above-mentioned species is briefly appraised. Of the remaining 16 species (7%) captured in light-traps 15 (6%) belong to that sector of the genus Culicoides whose immature stages develop in groundwater habitats and include C. imicola, which comprised only 2% of the light-trap collections. The large disparity in the adult abundance patterns of the "dung" and "groundwater" species in the middle of dry bushveld, is probably the result of differences in host and larval habitat preferences, and is briefly discussed. Finally, the few reports extant on the wild-host preferences of Afrotropical Culicoides are reviewed. Five tables and five figures accompany the text.