Variation of the vectorial capacity of some anophelines in western Venezuela

The vectorial capacities of Anopheles nuneztovari, An. albitarsis s.l., and An. triannulatus to transmit Plasmodium vivax in western Venezuela were estimated in different seasons. In general, there was a decrease in the vectorial capacities of the three species during the dry season, which seems to be due mainly to a reduction in the mosquito biting populations. Comparing the observations made during the two wet seasons, there was a decrease in the vectorial capacities of the three species due to different factors for each species. In An. nuneztovari, the reduction in vectorial capacity seems to be due to a reduction in the human blood index (HBI); in An. albitarsis, it is probably due to a reduction in the HBI and a slight reduction in parity, whereas in An. triannulatus, the cause is probably a reduction in the mosquito biting population and in parity. The overall reduction in vectorial capacities of the three anopheline species in 1989 compared with the vectorial capacities in 1988 could partly explain the marked reduction in prevalence from 46.2 per 1,000 population in 1988 to 7.5 per 1,000 population in 1989.