Direct and indirect selection pressures of insecticide resistance development in Anopheles and Culex mosquitoes

Although only pyrethroids with a few organophosphates are currently permitted as public health insecticides in South Korea, high frequencies of mutations conferring resistance not only to pyrethroids but also to cyclodienes and organophosphates have been observed in mosquitoes. Therefore, it remains to be elucidated whether non-public health insecticides drive selection pressure against mosquito species. In this study, to test the hypothesis that agricultural and industrial insecticides can play a role in selection, resistance profiles to three insecticide groups (pyrethroids, organophosphates, and cyclodienes) in two representative mosquito species (Anopheles sinensis and Culex pipiens) were investigated by analyzing the resistance allele frequencies of the kdr, acetylcholinesterase 1 (ace1) G119S mutation, and rdl. Subsequently, the correlation between the resistance allele frequency and the land use status of collection sites was analyzed. The kdr and rdl frequencies in An. sinensis showed a negative correlation with forest (r=-0.47 and r=-0.47, respectively), whereas the distance from golf club showed negative correlation with all three resistance alleles (r=-0.39, r=-0.42 and r=-0.44 respectively) perhaps due to insecticides used for turf maintenance. In the case of Cx. pipiens, the kdr, ace1 and rdl mutations showed positive correlation with residential area (r=0.53), rice paddy (r=0.59) and field (r=0.87), respectively. Therefore, it can be inferred that pyrethroids used for public health function as the main direct resistance selection pressure against kdr, whereas non-public health insecticides such as fipronil and carbamates may work as indirect selection pressure against ace1 and rdl mutations.