Insecticide Resistance Variation among Three Culex pipiens (Diptera: Culicidae) Populations in Egypt

Several studies have reported on insecticide resistance in mosquitoes; however, there is a lack of information about the resistance of Culex pipiens in Egypt. This study was conducted to investigate insecticide resistance status in three Cx. pipiens populations. These populations were collected from two rural breeding sites and one urban site in Egypt. Al-Beshlawy drainage canal and El-Khartoum irrigation ditch were selected to represent rural sites in Giza and Beheira governorates, respectively. One man-made ground hole was selected in Tanta, Gharbia Governorate, as an urban breeding site. Insecticide residues were analysed in water samples collected from the three breeding sites. Four insecticides, malathion chlorpyrifos, deltamethrin and fipronil, were tested against Cx. pipiens third-instar larvae of three field populations and one insecticide-susceptible (reference) population. Four insecticide residues and one additive (piperonyl butoxide) were detected; only malathion and piperonyl butoxide concentrations exhibited significant differences among all breeding sites. The level of malathion residue in the Giza breeding site was significantly higher than those in the Gharbia and Beheira breeding sites. According to the lethal concentrations (LC50) of the applied insecticides, the susceptibility of Cx. pipiens third-instar larvae to different insecticides demonstrated the order fipronil > chlorpyrifos > deltamethrin > malathion. Variations in the percentage mortality of Cx. pipiens were observed following malathion application between the Gharbia population and with both Giza and Beheira populations. Culex pipiens populations exhibited low resistance to most tested insecticides; however, the populations of Giza and Beheira exhibited moderate resistance to malathion. The variation in the resistance of Cx. pipiens populations to malathion could provide new information about the intraspecific variation among some mosquito populations in Egypt.