title: Over-expression of a cytochrome P450 is associated with resistance to pyriproxyfen in the greenhouse whitefly Trialeurodes vaporariorum.
abstract: BACKGROUND
  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. Although there are reports of insects evolving resistance to pyriproxyfen, the underlying resistance mechanism(s) are poorly understood.
  
  
  RESULTS
  Bioassays 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.
  
  
  CONCLUSIONS
  Over-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.
authors.affiliation: Rothamsted Research, Harpenden, Hertfordshire, United Kingdom. nikolaos.karatolos@rothamsted.ac.uk
authors.forename: Nikos
authors.initials: N
authors.lastname: Karatolos
authors.forename: Martin S
authors.initials: MS
authors.lastname: Williamson
authors.forename: Ian
authors.initials: I
authors.lastname: Denholm
authors.forename: Kevin
authors.initials: K
authors.lastname: Gorman
authors.forename: Richard H
authors.initials: RH
authors.lastname: Ffrench-Constant
authors.forename: Chris
authors.initials: C
authors.lastname: Bass
mesh_terms: D000818:Animals; D003577:Cytochrome P-450 Enzyme System / Q000235:genetics* / Q000502:physiology; D004791:Enzyme Inhibitors / Q000494:pharmacology; D006430:Hemiptera / Q000187:drug effects; D007305:Insecticide Resistance / Q000235:genetics*; D007306:Insecticides / Q000494:pharmacology; D007605:Juvenile Hormones; D010882:Piperonyl Butoxide / Q000494:pharmacology; D011725:Pyridines / Q000494:pharmacology*
chemical_list: D004791:Enzyme Inhibitors; D007306:Insecticides; D007605:Juvenile Hormones; D011725:Pyridines; C055613:pyriproxyfen; D003577:Cytochrome P-450 Enzyme System; D010882:Piperonyl Butoxide