title: Overexpressed esterases in a fenvalerate resistant strain of the cotton bollworm, Helicoverpa armigera.
abstract: Enhanced detoxification is the major mechanism responsible for pyrethroid resistance in Chinese populations of Helicoverpa armigera. Previous work has shown that enhanced oxidation contributes to resistance in the fenvalerate-selected Chinese strain, YGF. The current study provides evidence that enhanced hydrolysis by esterase isozymes also contributes to the resistance in this strain. The average esterase activity of third instar YGF larvae was 1.9-fold compared with that of a susceptible SCD strain. Much of this difference was attributed to isozymes at two zones which hydrolysed the model carboxylester substrate 1-naphthyl acetate and also a 1-naphthyl analogue of fenvalerate. A preparation enriched for enzymes migrating to one of these zones from YGF was shown to hydrolyse fenvalerate with a specific activity of about 2.9 nmol/min/mg. This material was also matched by mass spectrometry with four putative carboxylesterase genes, all of which clustered within a phylogenetic clade of secreted midgut esterases. Quantitative PCR on these four genes showed several-fold greater expression in tissues of YGF compared to SCD but no differences was found in the number of copies of the genes between the strains.
authors.affiliation: Department of Entomology, College of Plant Protection, Nanjing Agricultural University, Key Laboratory of Monitoring and Management of Crop Diseases and Pest Insects (Ministry of Agriculture), Nanjing 210095, China.
authors.forename: Shuwen
authors.initials: S
authors.lastname: Wu
authors.forename: Yihua
authors.initials: Y
authors.lastname: Yang
authors.forename: Guorui
authors.initials: G
authors.lastname: Yuan
authors.forename: Peter M
authors.initials: PM
authors.lastname: Campbell
authors.forename: Mark G
authors.initials: MG
authors.lastname: Teese
authors.forename: Robyn J
authors.initials: RJ
authors.lastname: Russell
authors.forename: John G
authors.initials: JG
authors.lastname: Oakeshott
authors.forename: Yidong
authors.initials: Y
authors.lastname: Wu
mesh_terms: D000595:Amino Acid Sequence; D000818:Animals; D002681:China; D004950:Esterases / Q000235:genetics* / Q000378:metabolism; D018628:Gene Dosage; D015870:Gene Expression / Q000187:drug effects; D017344:Genes, Insect; D006868:Hydrolysis / Q000187:drug effects; D007305:Insecticide Resistance / Q000187:drug effects / Q000235:genetics; D007306:Insecticides / Q000494:pharmacology; D007814:Larva / Q000201:enzymology; D013058:Mass Spectrometry; D008969:Molecular Sequence Data; D009036:Moths / Q000201:enzymology / Q000235:genetics*; D009280:Naphthaleneacetic Acids / Q000737:chemistry; D009570:Nitriles / Q000494:pharmacology; D010802:Phylogeny; D011722:Pyrethrins / Q000494:pharmacology
chemical_list: D007306:Insecticides; D009280:Naphthaleneacetic Acids; D009570:Nitriles; D011722:Pyrethrins; C034182:1-naphthaleneacetic acid; D004950:Esterases; C017690:fenvalerate