Submitted to: Journal of Economic Entomology
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 9/30/2011
Publication Date: 4/1/2012
Citation: Niu, G., Pollock, H.S., Lawrance, A., Siegel, J.P., Berenbaum, M.R. 2012. Effects of naturally occurring and synthetic synergists on the toxicity of three insecticides, a phytochemical and a mycotoxin to the navel orangeworm Amyelois transitella (Lepidoptera: Pyralidae). Journal of Economic Entomology. 105(2) 410-417. Interpretive Summary: When navel orangeworm feed on almonds and pistachios, they not only damage the nut but also increase the likelihood that these damaged nuts are colonized by fungi that produce toxins harmful to humans. If there were a chemical agent that both decreased the amount of insecticide needed to control navel orangeworm and decreased the level of these fungi, control of this insect would improve tremendously. Additionally, organic growers have fewer control options than conventional growers and an approved organic pesticide would be a welcome addition to the growers’ arsenal of insect control products. In this paper, we report that a natural plant-derived chemical, myristicin, can amplify or synergize the activity of a pyrethroid insecticide. In contrast, a known synthetic chemical synergist piperonyl butoxide, increased the activity of two pyrethroid insecticides and one plant toxin. Neither compound had an effect on Intrepid, a widely used selective insecticide. This indicates that Intrepid is detoxified by a different route. Considerably more research must be undertaken to document how navel orangeworm detoxifies the different insecticides and plant chemicals that it is exposed to in order to exploit vulnerabilities through design of better insecticides and/or choosing the most effective insecticide. Myrisiticin showed promise as a synergist in our experiments, and if it also kills toxin producing fungi, products containing myristicin may help organic growers.
Technical Abstract: The navel orangeworm is the most destructive lepidopteran pest of almonds and pistachios in California as well as a serious problem in figs and walnuts. Larval feeding leaves nuts vulnerable to infection by Aspergillus spp., fungi that produce toxic aflatoxins. A potentially safe and sustainable approach for managing navel orangeworm in orchards may be to use natural essential oil synergists to interfere with this insect’s ability to detoxify mycotoxins, phytochemicals and insecticides. We tested the effects of a naturally occurring plant-derived chemical, myristicin, and a synthetic inhibitor of cytochrome P450 monoxygenases (P450s), piperonyl butoxide, on the toxicity of three insecticides (a-cypermethrin, t-fluvalinate and methoxyfenozide), a phytochemical (xanthotoxin) and a mycotoxin, aflatoxin B1 to Amyelois transitella. The piperonyl butoxide and myristicin synergism bioassays with insecticides demonstrated that piperonyl butoxide significantly synergized cypermethrin and fluvalinate, while myristicin only synergized cypermethrin. Piperonyl butoxide synergized the toxicity of xanthotoxin over time while myristicin only slightly increased mortality at 7 d. None of the potential synergists tested enhanced aflatoxin B1 toxicity to larvae. In view of these findings and the limited availability of environmentally safe synthetic insecticides for sustainable management, particularly in organic orchards, myristicin is a potential field treatment to reduce both navel orangeworm survival and aflatoxin contamination of nuts.