STUDIES ON SUSCEPTIBILITIES OF BLACKFLIES TO INFECTIONS WITH THREE SPECIES OF BOVINE ONCHOCERCA

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Investigations were carried out at cattle sheds in Oita, Kumamoto and five other localites to clarify susceptibility or refractoriness of boviphilic Simulium and Culicoides to infections with three bovine Onchocerca species. As a result, Simulium bidentatum, S.arakawae, S.aokii, and S.daisense showed a complete susceptibility to O.sp., whereas S.daisense, S.arakawae and S.kyushuense were susceptible to O.lienalis. Only S.bidentatum was found to support O.gutturosa development to third-stage. In contrast, refractoriness was shown in S.bidentatum against O.lienalis and in S.kyushuense against O.sp. The former blackfly species was thought to interrupt development of O.lienalis microfilariae in the thorax, whereas the latter was observed to ingest no microfilariae of O.sp. All the eight Culicoides species examined did not harbor bovine Onchocerca larvae, although C.arakawae had third-stage larvae of unknown filaria which were similar to those of O.lienalis. The Onchocercalike microfilariae were rarely ingested only by C.matsuzawai. Overall, it is clarified for the first time that the susceptibility to bovine Onchocerca differs from one blackfly species to other. Further in certain blackfly species, it is shown to differ by the species of Onchocerca.