Afrotropical Culicoides : biosystematics of the imicola group. Subgenus Avaritia (Diptera : Ceratopogonidae)

Abstract

A biosystematic study of seven Afrotropical and two Oriental species of the Imicola species-group was undertaken; this group of Culicoides of the subgenus Avaritia includes C. imicola the most important vector of the viruses of bluetongue (BT) and African horsesickness (AHS) known in the Old World. Five African species are redescribed i.e. C. imicola, C. pseudopallidipennis, C. bolitinos, C. miombo and C. loxodontis. Two new species are described, and the extralimital C. brevitarsis and C. nudipalpis are discussed where relevant. These nine species comprise the Imicola group, one of 10 groups constituting the subgenus worldwide. Due to confusion in the literature, the Imicola group is redefined and distinguished from the Orientalis group (also redefined); 21 species of approximately 70 world species of Avaritia are reassigned to either of the two groups. A key to all nine known species of the lmicola group is given; shortcomings in the taxonomy of the Orientalis group are discussed. The adult morphology of both sexes of the nine Imicola group species was studied; this revealed deficiencies in the descriptive format currently used in taxonomic studies of world Culicoides. Accordingly, greater detail has been introduced into descriptions and includes the use of new character states. Methods for mounting Culicoides on glass slides are also improved to ensure more accurate observation and measurement of diagnostic taxonomic features; furthermore, the descriptions are based on long series of each sex. Illustrations were made from specimens mounted symmetrically, and no feature omitted from any bodypart illustrated. Certain aspects of the life-cycle of most species were investigated but especially those of C. bolitinos, C. loxodontis and C. kwagga. The immatures of these develop exclusively in the dung of the elephant, the buffalo, the blue wildebeest, both species of rhinoceros and Burchell's zebra. Two of these species, C. bolitinos and C. kwagga, have broadened their resource range as they can invade and mature in the dung of cattle and horses. This has obvious implications for the transmission of viruses, especially where indigenous herbivores are run with domesticated livestock. In an intensive two-year survey a comparison was made between the Culicoides fauna of a natural area, the Kruger National Park (KNP), and that found in areas changed by Man, namely livestock farms adjoining the KNP. This part of the eastern Transvaal lowveld is a main focus of AHS in South Africa. Light-trapping, rearing from dung, and pootering off live hosts, revealed that some species of the Imicola group are exclusively associated with certain herbivores; these include the elephant and the zebra which are suspected or proven reservoir hosts for AHS. The results thus throw further light on the epidemiology of this disease, and also show that Man plays a decisive role in determining the numbers, and distribution, of particular Imicola group species under certain conditions. In the case of C. imicola, the commonest and most widespread of all species, this range expansion, or establishment of foci, is due to man's maintenance of domesticated livestock in confined species, and especially where these are kept on irrigated pastures. However, the serendipitous discovery of a large imicola-free zone in South Africa indicates that edaphic conditions likely play an even more important role than Man and climate in determining the prevalence and abundance of C. imicola. This area is the sandy dune field west of Port Elizabeth and holds promise as a natural quarantine zone for the import and export of livestock. AFRIKAANS : 'n Biosistematiese ondersoek van sewe Afrotropiese en twee Orientale spesies van die Imicola groep is gedoen; by hierdie groep Culicoides van die subgenus Avaritia word C. imicola wat as die mees belangrikste vektor van bloutong-(BT) en perdesiekte (AHS) virus in die Ou Wereld beskou word, ingesluit. Vyf Afrika spesies, nl. C. imicola, C. pseudopallidipennis, C. bolitinos, C. miombo en C. loxodontis, is herbeskryf. Twee nuwe spesies is beskryf asook die suid-oos Asiese spesies C. brevitarsis en C. nudipalpis word bespreek waar van toepassing. Hierdie nege spesies vorm die Imicola groep, een van die 10 groepe waaruit die subgenus Avaritia wêreldwyd bestaan. As gevolg van verwarring in die literatuur is die Imicola groep hergedefinieer en geskei van die Orientalis groep ( ook hergedefinieer); 21 spesies van ongeveer 70 wereld spesies van Avaritia is heringedeel in die twee groepe. 'n Sleutel vir al nege wereld spesies van die Imicola groep, asook 'n verspreidingskaart vir elke spesie, word gegee. Tekortkominge in die taksonomie van die Orientalis groep word ook bespreek. Die volwasse morfologie van beide geslagte van die nege Imicola groep spesies is bestudeer; dit het gebreke in die formaat wat tans vir die taksonomiese beskrywing van wêreld Culicoides gebruik word aan die lig gebring. Gevolglik is daar meer data in die beskrywings, wat nuwe karakterkenmerke insluit. Die metode van die montering van Culicoides op glasplaatjies is ook verbeter om meer akkurate ondersoek en meting van die diagnostiese kenmerke te verseker; verder, is beskrywings gebaseer op lang reekse van elke geslag. Illustrasies is gemaak van voorbeelde wat simmetries gemonteer is en geen kenmerk is uitgelaat van enige gelllustreerde liggaamsdeel. Aspekte van die lewensiklus van die meeste van die spesies, veral C. bolitinos, C. loxodontis en C. kwagga is ondersoek. Die onvolwassenes van hierdie spesies ontwikkel slegs in die mis van olifante, buffels, wildebeeste, renosters en zebras. Twee van die spesies, C. bolitinos en C. kwagga, het hulle broeimediums van voorkeur vergroot en kan eiers lê en tot volwassenheid ontwikkel in die mis van beeste en perde. Dit het vanselfsprekende gevolge vir virusoordrag tussen inheemse herbivore en vee, veral in gebiede waar die twee groepe saamloop. In 'n intensiewe twee-jaar studie, is 'n vergelyking gemaak tussen die Culicoides fauna soos aangetref in 'n ongerepte deel van Afrika, die Kruger Nasionale Park (KNP), en in gebiede aangrensend aan die KNP wat deur die mens in veeplase omskep is. Die deel van die Oos Transvaalse laeveld is bekend as 'n perdesiekte "hotspot" in Suid-Afrika. Ligvalvangste, uitbroei van Culicoides uit mis en versameling vanaf lewendige gash ere het aangedui dat sekere spesies van die Imicola groep eksklusief met sekere herbivore geassosieeris; hierby ingesluit is die olifant en zebra wat onderskeidelik verdagte en bevestigde gashere van AHS is. Die resultate dra by tot die verklaring van die epidemiologie van hierdie siekte en wys ook dat die mens 'n beslissende rol speel in die vasstelling van die getalle sowel as die verspreiding van spesifieke spesies van die Imicola groep. In die geval van C. imicola, die mees algemeenste en wydverspreidste spesie, is die uitbreiding, of daarstelling van fokuspunte, te wyte aan die mens se instandhouding van vaste bloedbanke op besproeide weiding. Die toevallige ontdekking van 'n groot imicola-vry sone elders in Suid-Afrika dui daarop dat grondtipe moontlik 'n bepalende rol kan speel in die aanwesigheid en volopheid van C. imicola. Hierdie "skoon" area is die sandduine-veld wes van Port Elizabeth en lyk belowend as 'n natuurlike kwarantyn gebied vir die invoer en uitvoer van lewende hawe.