Published online by Cambridge University Press: 10 July 2009
Precipitin tests of the blood-meals of the non-anthropophilic population of Aedes simpsoni (Theo.) in Bwayise showed that at least 62% of the meals were mammalian; none was certainly avian or reptile. The remaining 38% were mostly too far digested for identification. Of the positive mammalian feeds, 84% were of rodents and only 5%; were of primates, probably human. In laboratory choice experiments, approximately two-thirds of a sample of the Bwayise strain fed on rodent in preference to monkey. Precipitin tests on blood-meals of the Bwamba strain of Ae. simpsoni confirmed earlier findings that this strain is strongly anthropophilic. At least 86% of wild-caught individuals had fed on mammals, 65% of these specifically identified: 28% of the feeds were of rodents and 72% were of primates, mostly human. During a five-month study at Bwayise in 1969, eleven species of rodents were caught; 91% of the rodents diurnally active were Arvicanthis niloticus which contributed 38% of the total collection and was twice as active during the afternoon as in the morning. The remaining species were predominantly nocturnal. A close relationship was found between the times of activity of A. niloticus and the biting cycle of Ae. simpsoni. In feeding tests using the three commonest rodent species, Ae. simpsoni selected A. niloticus as often as, or more often than, the nocturnal rodent species. This preference was maintained over one generation reared in culture. It is suggested that A. niloticus is the major natural host of the Bwayise strain by reason of the synchrony between rodent and mosquito activity rhythms. The Bwayise strain does not normally feed upon wild primates, so explaining further the almost total absence of human cases of yellow fever in areas of Uganda where this mosquito is non-anthropophilic.