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Title:Insecticide detoxification in the navel orangeworm Amyelois transitella (Lepidoptera: Pyralidae)
Author(s):Demkovich, Mark
Advisor(s):Berenbaum, May R.
Department / Program:Entomology
Degree Granting Institution:University of Illinois at Urbana-Champaign
Subject(s):Amyelois transitella
cytochrome P450 monooxygenase
Abstract:The polyphagous navel orangeworm (Amyelois transitella) is considered the most destructive pest of introduced nut crops, including almonds and pistachios, in California orchards. Management of this pest has typically been a combination of cultural controls (including removal of unharvested fruits) and the use of insecticides; insecticide use has increased substantially along with the value of these commodities. In a series of dietary studies the effects were assessed of the cytochrome P450 monooxygenase (P450) inhibitor piperonyl butoxide and the glutathione-S-transferase (GST) inhibitor diethyl maleate (DEM) on the toxicity of the insecticides azinphos-methyl, chlorpyrifos, chlorantraniliprole, β-cyfluthrin, and bifenthrin to first instar A. transitella larvae from a susceptible strain. Piperonyl butoxide (PBO) interacted antagonistically with the organophosphate insecticides azinphos-methyl and chlorpyrifos, indicating that they likely are bioactivated by P450s. Piperonyl butoxide synergized the toxicity of the pyrethroids β-cyfluthrin and bifenthrin, which suggests that P450s are involved in detoxification of pyrethroid insecticides. Only azinphos-methyl was a substrate for GSTs in A. transitella, as evidenced by diethyl maleate synergism assays. Neither PBO nor DEM influenced the toxicity of the anthranilic diamide chlorantraniliprole. Results suggest that if A. transitella detoxify other classes of insecticides used in management through enhanced P450 activity, and resistance begins to develop by this route, then incorporating organophosphate insecticides into rotations may provide an effective means of prolonging efficacy of chemical control because their speed of activation will increase. In a related series of studies to characterize a putatively pyrethroid-resistant strain of navel orangeworms, eggs from adults originating from almond orchards in which pesticide failures were reported in Kern County, California were shipped to the University of Illinois at Urbana-Champaign. Their susceptibility to bifenthrin and other pyrethroids was compared to that of an established colony of navel orangeworms. Administration of piperonyl butoxide and S,S,S-tributyl phosphorotrithioate (DEF) in bioassays with the pyrethroids bifenthrin and β-cyfluthrin produced synergistic effects and demonstrated that P450s and carboxylesterases (COEs) contribute to resistance in this navel orangeworm population. Resistance is therefore primarily metabolic and likely the result of overexpression of specific P450 and COE genes. Bioassays involving pesticides routinely used in tank mixtures indicate that chlorantraniliprole, which is not detoxified by P450s, may be more effective than methoxyfenozide in overcoming existing pyrethroid resistance because chlorantraniliprole enhanced pyrethroid toxicity and methoxyfenozide had no effect. Results from median-lethal concentration (LC50) assays revealed that resistance was maintained across eight generations in the laboratory. Life history trait comparisons between the resistant strain and susceptible strain revealed significantly lower pupal weights in resistant males and females reared on the same semi-synthetic diet across three generations. The number of days until the first molt was significantly greater in the resistant strain than the susceptible strain, although overall development time was not significantly different between strains. These experiments indicate that resistance is heritable and may have an associated fitness cost, which could influence the dispersal and expansion of resistant populations.
Issue Date:2014-05-30
Rights Information:Copyright 2014 Mark Demkovich
Date Available in IDEALS:2014-05-30
Date Deposited:2014-05

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