Mechanisms of Pyrethroid Resistance in the Dengue Mosquito Vector, Aedes aegypti: Target Site Insensitivity, Penetration, and Metabolism

• Published in: PLoS neglected tropical diseases Vol. 8; no. 6; p. e2948
• Main Authors: Kasai, Shinji, Komagata, Osamu, Itokawa, Kentaro, Shono, Toshio, Ng, Lee Ching, Kobayashi, Mutsuo, Tomita, Takashi
• Format: Journal Article
• Language: English
• Published: United States Public Library of Science 01.06.2014; Public Library of Science (PLoS)
• Subjects: Aedes - enzymology; Aedes - genetics; Alleles; Animals; Biology and Life Sciences; Cytochrome P-450 Enzyme System - genetics; Dengue fever; Female; Gene Dosage; Gene Knockdown Techniques; Gene mutations; Genetic aspects; Genetic Association Studies; Genotype; Identification and classification; Inactivation, Metabolic; Insect Proteins - genetics; Insecticide resistance; Insecticide Resistance - genetics; Insecticides; Insecticides - metabolism; Larva - enzymology; Larva - genetics; Male; Metabolism; Metabolites; Mosquito Control; Mosquitoes; Permethrin - metabolism; Sequence Analysis, DNA
• ISSN: 1935-2735; 1935-2727; 1935-2735
• DOI: 10.1371/journal.pntd.0002948

Aedes aegypti is the major vector of yellow and dengue fevers. After 10 generations of adult selection, an A. aegypti strain (SP) developed 1650-fold resistance to permethrin, which is one of the most widely used pyrethroid insecticides for mosquito control. SP larvae also developed 8790-fold resistance following selection of the adults. Prior to the selections, the frequencies of V1016G and F1534C mutations in domains II and III, respectively, of voltage-sensitive sodium channel (Vssc, the target site of pyrethroid insecticide) were 0.44 and 0.56, respectively. In contrast, only G1016 alleles were present after two permethrin selections, indicating that G1016 can more contribute to the insensitivity of Vssc than C1534. In vivo metabolism studies showed that the SP strain excreted permethrin metabolites more rapidly than a susceptible SMK strain. Pretreatment with piperonyl butoxide caused strong inhibition of excretion of permethrin metabolites, suggesting that cytochrome P450 monooxygenases (P450s) play an important role in resistance development. In vitro metabolism studies also indicated an association of P450s with resistance. Microarray analysis showed that multiple P450 genes were over expressed during the larval and adult stages in the SP strain. Following quantitative real time PCR, we focused on two P450 isoforms, CYP9M6 and CYP6BB2. Transcription levels of these P450s were well correlated with the rate of permethrin excretion and they were certainly capable of detoxifying permethrin to 4'-HO-permethrin. Over expression of CYP9M6 was partially due to gene amplification. There was no significant difference in the rate of permethrin reduction from cuticle between SP and SMK strains.