Efficacy of some insecticides on field populations of Culex pipiens (Linnaeus) from Egypt

The efficacy of the most used insecticides belonging to different groups (organophosphate, carbamate, synthetic pyrethroid and insect growth regulator) was tested against four different field populations of Culex pipiens. Results obtained showed that the laboratory colony showed higher susceptibility to the tested insecticides than the mosquito populations collected from Sharkia and Assiut Governorates. Field populations of Cx. pipiens from Sharkia were chosen to study the development of resistance (resistant strain) in Cx. pipiens to chlorpyrifos toxicity. After 15 generations of selection pressure using chlorpyrifos against the 3rd instar larvae of Cx. pipiens, resistance increased by 24.56-fold in the resistant strain as compared with the control. Fractionation of total soluble proteins using SDS–PAGE revealed some differences in the laboratory colony, field populations and resistant strain. Results may indicate that alkaline phosphatase and non-specific esterases were probably responsible for the detoxification of chlorpyrifos in field populations.