Abstract
BackgroundThe juvenile hormone mimic, pyriproxyfen is a suppressor of insect embryogenesis and development, and is effective at controlling pests such as the greenhouse whitefly Trialeurodes vaporariorum (Westwood) which are resistant to other chemical classes of insecticides. Although there are reports of insects evolving resistance to pyriproxyfen, the underlying resistance mechanism(s) are poorly understood.ResultsBioassays against eggs of a German (TV8) population of T. vaporariorum revealed a moderate level (21-fold) of resistance to pyriproxyfen. This is the first time that pyriproxyfen resistance has been confirmed in this species. Sequential selection of TV8 rapidly generated a strain (TV8pyrsel) displaying a much higher resistance ratio (>4000-fold). The enzyme inhibitor piperonyl butoxide (PBO) suppressed this increased resistance, indicating that it was primarily mediated via metabolic detoxification. Microarray analysis identified a number of significantly over-expressed genes in TV8pyrsel as candidates for a role in resistance including cytochrome-P450 dependent monooxygenases (P450s). Quantitative PCR highlighted a single P450 gene (CYP4G61) that was highly over-expressed (81.7-fold) in TV8pyrsel.ConclusionOver-expression of a single cytochrome P450 gene (CYP4G61) has emerged as a strong candidate for causing the enhanced resistance phenotype. Further work is needed to confirm the role of the encoded P450 enzyme CYP4G61 in detoxifying pyriproxyfen.
Highlights
Insecticide resistance in crop pests usually arises via one of two types of mechanisms: either reduced binding of the insecticide to its target through mutation of the target site [1], or increased detoxification or sequestration of insecticides [1,2] by enzymes such as carboxylesterases (CEs) [3], glutathione-S-transferases (GSTs) [4] and cytochrome P450 dependent monooxygenases (P450s)-dependent monooxygenases [5].Pyriproxyfen (2-[1-methyl-2-(4-phenoxyphenoxy)-ethoxy] pyridine) is a juvenile hormone analogue (JHA) effective against some arthropod pests including the greenhouse whitefly Trialeurodes vaporariorum Westwood and the sweet potato whitefly, Bemisia tabaci Gennadius (Hemiptera: Aleyrodidae)
Pyriproxyfen is a potent suppressor of embryogenesis and later development that competes for juvenile hormone receptor binding sites and disrupts the transition from one developmental stage to another [6,7,8]
Resistance to pyriproxyfen was first documented in B. tabaci from Israel in 1998 [11,12] and early studies suggested that P450s were not involved in the catabolism of pyriproxyfen [13]
Summary
Pyriproxyfen (2-[1-methyl-2-(4-phenoxyphenoxy)-ethoxy] pyridine) is a juvenile hormone analogue (JHA) effective against some arthropod pests including the greenhouse whitefly Trialeurodes vaporariorum Westwood and the sweet potato whitefly, Bemisia tabaci Gennadius (Hemiptera: Aleyrodidae). Pyriproxyfen is a potent suppressor of embryogenesis and later development that competes for juvenile hormone receptor binding sites and disrupts the transition from one developmental stage to another [6,7,8]. The juvenile hormone mimic, pyriproxyfen is a suppressor of insect embryogenesis and development, and is effective at controlling pests such as the greenhouse whitefly Trialeurodes vaporariorum (Westwood) which are resistant to other chemical classes of insecticides. There are reports of insects evolving resistance to pyriproxyfen, the underlying resistance mechanism(s) are poorly understood
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