A New Esterase Amplification Involved in OP Resistance in Culex Pipiens Mosquitoes from Tunisia

The linearity of dose–mortality responses was accepted (Chi square analysis P > 0.05) for S-Lab and Jendouba population (slope regression is 3.42 for S-Lab with Heterogeneity factor equal to 1 and 2.15 for Jendouba population with Heterogeneity factor equal to 5.01). RR at LC50 (RR50) showed that the sample was resistant to chlorpyrifos. The RR50 reached very high level with chlorpyrifos (RR50 = 8062 with confidence limits between 7759.46 and 8285.87). Addition of DEF to chlorpyrifos bioassays did not decrease tolerance significantly (P > 0.05) in S-Lab and Jendouba sample. So, the increased detoxification by EST (and/ or glutathione-s-transferases) was not involved in chlorpyrifos resistance of this sample. However, as reported by Ben Cheikh, et al. [12] the mosquito Culex pipiens esterases contributed to OP resistance by their increased activity. Likewise AChE was not involved in chlorpyrifos resistance.