Chapter 3 Insecticide Resistance in the Mosquito Culex pipiens Complex: Concerns about development of pyrethroid resistance

摘要

We investigated insecticide susceptibility of the mosquito Culex pipiens complex in Japan, using a total of 56 field-collected colonies of Cx. pipiens molestus, Cx. p. pollens, and Cx. quinquefasciatus. In 4 larvicides bioassayed (fenitrothion, etofenprox, diflubenzuron, and pyriproxyfen), obviously reduced susceptibilities were observed for a pyrethroid etofenprox. Twenty-two colonies exhibited over 10% survival rates at 5.7 μg/ml etofenprox concentration, which is 10 times higher than the practical concentration. Etofenprox resistant strains of Cx. p. m. and Cx. p. pallens were established by larval selections in the laboratory. The selected strains exhibited 10~3 order etofenprox resistance and also cross resistance to permethrin and phenothrin. The major mechanisms of pyrethroid resistance in these strains were both increased detoxifying activities of cytochrome P450 monooxygenases and kdr mutations in the sodium channel gene, kdr mutations identified from Cx. p. m. and Cx. p. pollens were L1014F and L1014S, respectively. Microarray analysis was conducted, targetting larval gene expressions of 62 different cytochrome P450 isoforms, using pyrethroid resistant JPP strain and a susceptible strains of Cx. q. Two extraordinarily highly expressing P450 genes, CYP9M10 and CYP4H34, were identified in JPP. The larva-specific expressions of the two P450 genes in JPP mosquitoes conformed to a great decrease in permethrin-resistance in adults, suggesting these isoforms are ? likely involved in pyrethroid detoxification.