Submitted to: Journal of Pest Science
Publication Type: Peer reviewed journal
Publication Acceptance Date: 2/15/2014
Publication Date: N/A
Citation: Interpretive Summary: The navel orangeworm is the primary moth pest of almonds and pistachios in California. Inexpensive pyrethroid insecticides play an increasingly important role in controlling this insect in nut crops. Navel orangeworm larvae encounter many different chemicals produced by plants when feeding, and these plant-produced chemicals (phytochemicals) may interact with insecticides. Quercetin (found in nut meats) and chlorogenic acid (found in almond hulls), when combined with the pyrethroid insecticide a-cypermethrin in laboratory tests, diminished the activity of a-cypermethrin by approximately 20% over 48 hours, resulting in surviving larvae. From a crop protection perspective, increased larval survival during the first 48 hours of exposure would increase feeding damage to almonds and feeding, in addition to destroying the kernel, increases the likelihood that the nut could be successfully colonized by aflatoxin-producing fungi. If aflatoxins are present above a level specified by law, the shipment containing contaminated nuts is rejected and cannot be sold. Because there are usually lower levels of insecticide in the upper canopy of almond trees, due to difficulties with spray coverage, increased larval survival due to a combination of the protective effect of phytochemicals and decreased levels of insecticide in the upper almond canopy could produce sporadic control failures. Understanding how eating quercetin and/or chlorogenic acid interferes with the activity of a-cypermethrin will help researchers develop more effective management strategies to control navel orangeworm and reduce crop damage.
Technical Abstract: Inexpensive pyrethroid insecticides (IRAC Group 3A) play an increasingly important role for control of navel orangeworm in almonds and other nut crops. In addition to the insecticides used for their control, navel orangeworm larvae encounter a broad diversity of phytochemicals in their host plants. The effects of simultaneous ingestion of both phytochemicals and insecticides on toxicity may be synergistic/additive, antagonistic, or neutral. To assess the effect of two almond phytochemicals on tolerance of navel orangeworm to pyrethroid insecticides, first instar larvae were fed chlorogenic acid, quercetin and a-cypermethrin alone and in combination and monitored in toxicity bioassays. When combined with a-cypermethrin, quercetin and chlorogenic acid, found in almond nutmeats and hulls respectively, reduced the effect of this insecticide by approximately 20%. Chlorogenic acid was more protective than quercetin for the first 36 h, but from that time point until 48 h their effect was similar. From a crop protection perspective, decreased efficacy of a pyrethroid insecticide in the presence of phytochemicals suggests that the ability of navel orangeworm larvae to survive and feed for 48 h may lead to economic damage on almond kernels; moreover, the combination of lower insecticide levels in the upper canopy of almonds, combined with the antagonistic effect of phytochemicals present in almonds, may produce sporadic control failures. Identification of the mechanism underlying the antagonistic interaction between quercetin, chlorogenic acid and a-cypermethrin can help researchers develop more effective management strategies to control navel orangeworm and reduce damage.