First Report of Biochemical Mechanisms of Insecticide Resistance in the Field Population of Culex pipiens (Diptera: Culicidae) From Sari, Mazandaran, North of Iran

Background: Culex pipiens play an important role in transmission of infectious diseases. Vector control by chemi­cal pesticides, leads inevitably to resistance development. Understanding the underlying resistance mechanisms can help improve the control programmes and insecticide resistance management. Methods: The total contents of cytochrome p450s and the activities of glutathione S-transferases, alpha- and beta-esterases and inhibition rates of acetylcholine esterase (by propoxur) were measured in the field population of Cx. pipiens collected from Sari County, North of Iran, in 2016 and the results were compared with those of the laborato­ry susceptible strain according to the biochemical assay methods of WHO for adult mosquitoes. Independent sample t-test was used to compare the mean values of enzyme activities/contents between filed and laboratory susceptible popula­tions. Results: The enzyme ratio of cytochrome p450s, alpha- and beta-esterases in the field population was 2.07, 3.72 and 1.36 respectively when compared with the results of the laboratory population. Although not statistically significant, the mean GSTs activities in the field population was marginally less than the laboratory population (ER=0.92). Ace­tylcholinesterase was insensitive to propoxur in 62.82% of the individuals of the tested field population. There was a significant difference (P< 0.05) between all values of the activities/contents of the enzyme in the field population except for GSTs compared with the laboratory susceptible strain. The highest enzyme activity was related to alpha esterase. Conclusion: The present study showed a range of metabolic mechanisms, comprising p450s and esterases combined with target site insensitivity of AChE, contributing to organophosphate, carbamate and pyrethroid resistance in the field population of Cx. pipiens.