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Spodoptera lituraFabricius (Lepidoptera: Noctuidae) is one of the most destructive pests of various crops cultivated in Thailand. Spodoptera lituralarvae, at early stages, attack the leaves and feed on every part of infested crops in later stages. Acorus calamusessential oil contains toxic asarones, which are generalistic cytotoxic compounds. However, the present study is the first attempt to look at safer metabolites from the rhizomes that could deter insect feeding. The objective was to use such compounds as safer residues on crops that would prevent the feeding of herbivorous lepidopterans. Accordingly, phenolic metabolites were isolated and evaluated to establish the feeding deterrence against polyphagous S. lituralarvae. Methanol extract of A. calamus, chrysin, and 4-hydroxy acetophenone compounds were the most effective feeding deterrents with FD50of 87.18, 10.33, and 70.77 µg/cm2, respectively, after 4 h of feeding on treated kale leaves in a no-choice leaf disc assay. Chrysin also reduced carboxylesterase activities (1.37-fold), whereas A. calamusmethanol extract reduced glutathione-S-transferase activities (1.44-fold). Some larvae were also seen dead if they consumed the treated kale leaves. Feeding deterrent activity in the methanol extract of A. calamuswas due to chrysin and 4-hydroxy acetophenone. The large-scale utilization of such compounds could help develop feeding deterrent strategies in the integrated pest management of lepidopterans.Graphical Abstract

This article reports the current status of ethiprole resistance in Nilaparvata lugensStål in the central region of Thailand, together with the associated resistance mechanisms. A resistance survey found that a field population had developed 308.5-fold resistance to ethiprole. Further selection with ethiprole for nine generations in the laboratory led to 453.1-fold ethiprole resistance. However, following this selection procedure, the resistance ofN. lugensto other insecticides decreased to about one-third of its original resistance. This result implies that there is no cross-resistance between ethiprole and other kinds of insecticides in this pest. In an in vivo study of synergisms, triphenyl phosphate (TPP) exhibited a strong synergism (SR 4.2) with ethiprole in the resistant hoppers, piperonyl butoxide (PBO) also showed significant synergistic effects with ethiprole (1.6), but diethyl maleate (DEM) did not show any obvious synergism with ethiprole (1.2). An in vitro biochemical study indicated that esterase activity increased with ethiprole resistance in N. lugens, that P450 monooxygenase activity also increased significantly with high resistance, but that glutathioneS-transferase activity did not. These results reveal that increases in esterase activity and P450 monooxygenase activity cause the ethiprole resistance observed in the field populations of N. lugens. Whether the mechanisms for ethiprole resistance involve target-site sensitivity is not yet known; further molecular analysis is required. However, an analysis of insecticide cross-resistance and the insecticide application history of the resistant populations indicated that target resistance was present and that rotation between insecticides with different modes of action will provide a key countermeasure to maintain the efficacy of ethiprole.