Continuous data collected over the last 10 years in a forested mountain area in central/south Vietnam showed that Anopheles dirus is the only important vector responsible for persistent malaria transmission and is very difficult to control. This deep forest mosquito prefers to bite humans and does so early in the evening. Although the population size of An. dirus is not so large
it can appear in large numbers where people overnight in the forest and can fly more than 2,000 m to find its prey. The ecological characteristics of An. dirus allow it to evade most kinds of chemical control methods although the application of repellent cream with DEET can greatly reduce bites in forest. Up till now, no other method showed practical effectiveness In bite prevention from this mosquito. For the first time in Vietnam it has been shown that An. dirus also carries sporozoites of Plasmodium knowlesi, a monkey .malaria parasite that can aIso infect humans, This presents a new challenge to malaria control in the forest.