The mosquitoes responsible for malaria transmission to humans belong to the Anopheles genus. One of the best known and most extensively studied is Anopheles gambiae, Africas principal malaria vector. The protection recommended by the World Health Organization for people at risk from this devastating disease is the use of mosquito nets impregnated with pyrethroids, of low toxicity for mammals and highly active against mosquitoes. Unfortunately, excessive and inappropriate use of this family of insecticide, particularly by spraying, has induced a disturbing rise in the number of resistant individuals in the Anopheles populations. The mosquito nets treated with pyrethroids can therefore lose their effectiveness. It is therefore essential to devise new control strategies against these malaria vectors that are resistant to these insecticides.
IRD researchers and their partners (1) obtained encouraging results by combining a non-pyrethroid insecticide, propoxur, and a repellent, N,N-diethyl toluamide (DEET). They based their investigations on previous work which had revealed a strong synergy between the two components. A combination of the two had proved to be much more effective than the straightforward addition of their respective properties. Mosquito nets soaked with this mixture had a lethal power and irritant effect that inhibited the mosquitoes from biting. Moreover, the mosquitoes are hit by a powerful paralysing action, known as the knockdown effect (3), on contact with the mixture. The mortality rates determined were satisfactory, in that they equalled those obtained by using deltamethrin, a commonly-used synthetic pyrethroid, highly effective against mosquitoes.
The researchers tested two mixtures composed of a non-pyrethroid insecticide of the organophosphate family, combined with either a standard repellent, DEET, or with a new-generation synthetic repellent. Both of these mixtures show a strong synergy in the resulting lethal and paralysing
Contact: Gregory Flechet
Institut de Recherche Pour le Dveloppement