Study of irritant effect of Permethrin impregnated nets on Pyrethroid resistant and susceptible genotypes of the mosquito Anopheles Stephensi

Pyrethroid-impregnated bednets have been shown to be one of the most promising tools that have emerged in recent years to control malaria. Mosquitoes may be physically irritated by pyrethyroids, reducing the time searching for blood meals, or driving them away. Permethrin impregnated nets also may deter a proportion of mosquitoes from entering houses. Irritant effect of nets treated with 200 mg and 500 mg permethrin/m² on susceptible and resistant genotypes of Anopheles stephensi was studied using the modified W.H.O. provisional technique. The W.H.O. irritability test was not used in the present study. Irritability test were carried out in a W.H.O. plastic bioassay cone. Three days old unfed, females were tested individually or in group of five mosquitoes. When female mosquitoes were confined in bioassay cones on treated netting, the resistant strain of A.stephensi showed significantly less irritability (Scored on the time until first flight take-off) in response to each dose as compared with the susceptible strain and F1 hybrids. The higher dose provoked more irritation of each genotypes, this could cause lower knockdown and kill rates which this dose could produce with each genotype. From the results of this study it could be concluded that a dose of 200 mg/m² of permethrin impregnated into bednets is preferable to 500 mg/m² for malaria control.