Sublethal insecticide exposure of larvae affects the blood-feeding behaviour of adult mosquitoes.

BACKGROUND: Due to their widespread use for controlling disease vectors and agricultural pests, insecticides have become ubiquitous in the environment, including in water bodies harbouring mosquito larvae. As a result, these larvae are continuously exposed to sublethal doses. Since this has long-lasting effects on the mosquitoes' physiology and life-history, we expected that it may also affect behaviours that underlie the mosquitoes' population dynamics and disease epidemiology, such as egg-laying preference, blood-feeding motivation and host-seeking behaviour.

METHODS: Using an insecticide-sensitive and a resistant strain of Anopheles gambiae, an important malaria vector, we evaluated the effects of sublethal exposure to permethrin throughout larval development on the resistance to the insecticide in adults, on host-seeking behaviour, on the motivation to blood-feed and on egg-laying behaviour.

RESULTS: Exposure to sublethal doses of insecticide did not affect knock-down or mortality rates. However, it decreased the avoidance of permethrin-treated nets, and it increased the motivation of females to seek blood meals through permethrin-treated nets, regardless of their sensitivity to the insecticide. It also increased the blood-meal size in particular of the sensitive mosquitoes. Finally, exposed females were more likely than unexposed ones to lay their eggs into several sites.

CONCLUSIONS: Sublethal insecticide exposure during larval development changes several aspects of the behaviour of mosquitoes in ways that could enhance disease transmission and may thus have significant epidemiological implications.