Résumé
Background : The control of most vectors of malaria is threatened by the spread of insecticide resistance. Onefactor that has been hitherto largely overlooked is the potential effects of insecticide resistance on the ability ofmosquitoes to transmit malaria : are insecticide-resistant mosquitoes as good vectors of Plasmodiumas susceptibleones ? The drastic physiological changes that accompany the evolution of insecticide resistance may indeed alterthe ability of vectors to transmit diseases, a possibility that, if confirmed, could have major epidemiological consequences. Methods : Using a novel experimental system consisting of the avian malaria parasite (Plasmodium relictum) and itsnatural vector (the mosquito Culex pipiens), two of the most common mechanisms of insecticide resistance (esterase overproduction and acetylcholinesterase modification) were investigated for their effect on mosquitoinfection rate and parasite burden. For this purpose two types of experiments were carried out using (i) insecticide-resistant and susceptible laboratory isogenic lines of Cx. pipiensand (ii) wild Cx. pipienscollected from a populationwhere insecticide resistant and susceptible mosquitoes coexist in sympatry. Results : The isogenic line and wild-caught mosquito experiments were highly consistent in showing no effect ofeither esterase overproduction or of acetylcholinesterase modification on either the infection rate or on the oocystburden of mosquitoes. The only determinant of these traits was blood meal size, which was similar across thedifferent insecticide resistant categories in both experiments.Conclusions:Insecticide resistance was found to have no effect onPlasmodiumdevelopment within the mosquito.This is the first time this question has been addressed using a natural mosquito-Plasmodiumcombination, whiletaking care to standardize the genetic background against which the insecticide resistance genes operate. Infectionrate and oocyst burden are but two of the factors that determine the vectorial capacity of mosquitoes. Other keydeterminants of parasite transmission, such as mosquito longevity and behaviour, or the parasite’s incubation time, need to be investigated before concluding on whether insecticide resistance influences the ability of mosquitoesto transmit malaria.