Pyrethroid insecticides induce an excito-repellent effect that reduces contact between humans and mosquitoes.
Insecticide use is expected to lower the risk of pathogen transmission, particularly when impregnated on long-lasting treated bednets. When applied at low doses,
pyrethroids have a toxic effect, however the development of
pyrethroid resistance in several mosquito species may jeopardize these beneficial effects. The need to find additional compounds, either to kill disease-carrying mosquitoes or to prevent mosquito contact with humans, therefore arises. In laboratory conditions, the effects (i.e., repellent,
irritant and toxic) of 20
plant extracts, mainly
essential oils, were assessed on adults of Anopheles gambiae, a primary vector of
malaria. Their effects were compared to those of
DEET and
permethrin, used as positive controls. Most
plant extracts had
irritant, repellent and/or toxic effects on An. gambiae adults. The most promising extracts, i.e. those combining the three types of effects, were from Cymbopogon winterianus, Cinnamomum zeylanicum and Thymus vulgaris. The
irritant, repellent and toxic effects occurred apparently independently of each other, and the behavioural response of adult An. gambiae was significantly influenced by the concentration of the
plant extracts. Mechanisms underlying repellency might, therefore, differ from those underlying irritancy and toxicity. The utility of the efficient
plant extracts for vector control as an alternative to
pyrethroids may thus be envisaged.