Multiple host feeding in field populations of Anopheles culicifacies and An. subpictus in Sri Lanka.

A histological technique was used to detect the multiple blood-feeding of female mosquitoes, within the same gonotrophic cycle, in field populations of the malaria vectors Anopheles culicifacies and An. subpictus (Diptera: Culicidae) at a village in the low country of Sri Lanka, during 1994-96. Among 3306 An. culicifacies and 871 An. subpictus engorged females examined, respectively, 34.4% and 30.4% were multiple-fed. In these two species, double meals accounted for 92.7% and 89.5%, and triple meals for 7.3% and 10.5% of multiple meals, respectively. More females of An. culicifacies (53.7%) than An. subpictus (44.5%) multiple-fed on different nights. Multiple feeding rates in the two species were independent of sample size and field abundance. In An. culicifacies, but not An. subpictus, these rates were proportional to ambient temperature but not to humidity. Bloodmeal ELISA showed that 8.3% of 242 An. culicifacies were human-fed and 80% of these (i.e. 6.6%) were concurrently bovid-fed. Combining the histological and ELISA data, it was estimated that multiple feeding involving a human host had occurred in 7.2% of the blood-feeding An. culicifacies population at this study site. Only 1.2% of 406 An. subpictus were human-fed and all of these were concurrently bovid-fed. Multiple bloodfeeding within the same gonotrophic cycle was attributed to a local 'frequent feeding strategy' in these primarily zoophagic and endophilic malaria vectors. Unfortunately this strategy enhances their human-biting rate and hence their vectorial capacity.