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

Abstract

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.

Evaluation of larvicidal activity of a nanoemulsion of Rosmarinus officinalis essential oil

“…Further characterization revealed that narrow distribution was achieved, probably due to disintegration and regeneration of micelles. Penetration through cuticle is crucial for insecticidal activity and recognized as one of possible mechanisms of insectides (Kasai et al, 2014). Considering that particle size of droplets remained in a nanometric range, penetration and potential larvicidal activity may not be affected.…”

An analysis of community perceptions of mosquito-borne disease control and prevention in Sint Eustatius, Caribbean Netherlands

“…Permethrin is used as the primary chemical when fogging and is the only chemical on the market that can be legally used. Continuous fogging would ultimately result in mosquitoes becoming resistant and fogging becoming ineffective in the long term [37,38]. Furthermore, fogging can cause damage to the local fauna on the island.…”

Identifying genomic changes associated with insecticide resistance in the dengue mosquito Aedes aegypti by deep targeted sequencing

“…Several amplified CYP9Js were previously found overtranscribed in resistant populations and some of them (CYP9J24, CYP9J28, CYP9J32) have been validated as able to metabolize pyrethroids (Stevenson et al 2012), supporting the importance of their amplification in resistance. Among the CYP6s amplified, most were previously found overtranscribed in resistant populations, and CYP6BB2 was recently involved in pyrethroid metabolism (Kasai et al 2014). In addition, some of their close orthologs in Anopheles (CYP6P3, CYP6P7, CYP6P9, CYP6M2, and CYP6AA5) are also capable of degrading pyrethroids (Boonsuepsakul et al 2008;Müller et al 2008;Duangkaew et al 2011;Stevenson et al 2011;Riveron et al 2013).…”