Studies onOnchocerca gutturosa(Neumann, 1910) and its Development inSimulium Ornatum(Meigen, 1818). 3. Factors Affecting the Development of the Parasite in its Vector

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Abstract
1. Observations were made on various methods of infecting S.ornatumwith 0.gutturosa, the behaviour of the parasite in its vector, and the maintenance of the vector in the laboratory.2. S.ornatumreared from pupae brought into the laboratory were successfully infected with 0.gutturosaafter feeding on infected cattle. The use ofin vitromethods of infection was unsuccessful as microfilariae were ingested but did not undergo larval development.3. The migratory route of 0.gutturosamicrofilariae ingested by S.ornatumwas studied and it was found that a mean of only 25% penetrate out of the abdominal midgut. The dimensional changes of 0.gutturosawere noted from the time of ingestion by S.ornatumuntil the infective stage was reached.4. 0.gutturosatook 13–15 days to reach the infective stage in S.ornatumwhen maintained at a constant temperature of 23°C.5. The development and structure of the peritrophic membrane of S.ornatumare described.6. Preliminary observations on the seasonal variations of some factors affecting the transmission of O.gutturosaby S.ornatumsuggest that microfilariae were only available for ingestion during the period of vector activity, after which they migrated into the deeper regions of the skin of cattle.