|DEMKOVICH, MARK - University Of Illinois
|DANA, CATHERINE - University Of Illinois
|BERENBAUM, MARY - University Of Illinois
Submitted to: Journal of Economic Entomology
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 6/6/2015
Publication Date: 8/9/2015
Citation: Demkovich, M., Dana, C.E., Siegel, J.P., Berenbaum, M.R. 2015. Effect of piperonyl butoxide on the toxicity of four classes of insecticides to navel orangeworm (Amyelois transitella)(Lepidoptera: Pyralidae). Journal of Economic Entomology. 108(6):2753-2760.
Interpretive Summary: The navel orangeworm, Amyelois transitella, is the most destructive pest of almonds and pistachios grown in California. These two crops are planted on approximately 1.3 million acres and have a direct value to the grower of more than $8.5 billion. Insect damage is controlled by a combination of methods including field sanitation and insecticide use when necessary. As the value of these crops has increased, so has insecticide use. This increased useage/reliance on insecticides in turn increases the likelihood that insecticide resistance will develop. In order to prevent insecticide resistance or slow down its development, it is essential to understand how the navel orangeworm detoxifies the different familes of insecticides used for its control in tree nut crops. One major insecticide detoxification pathway involves a family of enzymes known as cytochrome P450 monooxygenases. These enzymes can either break down an insecticide by oxidation, thereby reducing its activity, or the process of oxidation actually activates toxicity. In this paper we determined which families of insecticides used to control navel orangeworm were broken down by the cytochrome P450 system, by adding a chemical that inhibits this system (piperonyl butoxide). If the toxicity of an insecticide increased when the inhibitor was added, then the P450 system is involved in its detoxification, and if the toxicity decreased when the inhibitor was added, then cytochrome P450 enzymes are needed to activate the insecticide. If there was no change in toxicity when the inhibitor was added, a different system is involved in detoxification. Five families of insecticide were tested and the cytochrome P450 system detoxified three families: pyrethroid, neonicitinoid, and spinosad. This system activated one family, the organophosphates, and had no effect on diamide insecticides, which affect insect muscles. This information is the first step needed to develop rotation strategies to preserve the use of these insecticide families to control navel orangeworm.
Technical Abstract: Navel orangeworm, Amyelois transitella (Walker) (Lepidoptera: Pyralidae), is a highly polyphagous economic pest of almond, pistachio, and walnut crops in California orchards. Although management of this pest has typically been through a combination of cultural control and insecticide sprays, increasing demand for these crops combined with their rising value has resulted in substantial increases of insecticide applications to reduce damage to acceptable levels. The effects of the cytochrome P450 monooxygenase inhibitor piperonyl butoxide (PBO) on the toxicity of the insecticides acetamiprid, chlorpyrifos, chlorantraniliprole, lambda-cyhalothrin, and spinosad were assessed in a series of bioassays with first instar A. transitella larvae from a laboratory strain. PBO interacted antagonistically with the organophosphate insecticide chlorpyrifos, reducing its toxicity, indicating that this organophosphate is likely bioactivated by P450s. In contrast, PBO synergized the toxicity of acetamiprid, lambda-cyhalothrin, and spinosad, results that implicate P450s in the detoxification of at least some representative neonicotinoid, pyrethroid, and spinosyn insecticides. The toxicity of the anthranilic diamide insecticide chlorantraniliprole was not altered by PBO. Because a population of navel orangeworm in Kern County, CA has already developed resistance to the pyrethroid insecticide bifenthrin through enhanced P450 activity, it is crucial to determine the extent to which P450s are involved in detoxification of all insecticide classes registered for use in navel orangeworm management and to develop rotation practices that may delay resistance acquisition by reducing selection pressure on P450-mediated detoxification pathways.