Explore the vast range of titles available.

The brown planthopper (BPH) Nilaparvata lugens (Stål) is a major insect pest of Oryza sativa that causes crop yield loss in tropical regions, including Thailand. In this study, the crude ethanolic extract of the leaves and branches of Combretum trifoliatum , its active isolated components, apigenin and camphor, and Finopril were tested for their ability to control the first to fifth instars of N. lugens. The C. trifoliatum crude extract and both allelochemicals showed insecticide potential (24 h-LC50 ~ 8.83–95.96 mg/L against each instar for crude extract), and their toxicity depended on the time of exposure. Camphor showed the higher efficacy (LD50 ~ 4.43 mg/L) and not different compared to Finopril. All plant compounds tested reduced carboxylesterase (CE) and glutathione-s-transferase (GST) activities. Camphor caused the greatest decreases in CE and GST activities after exposure, whereas apigenin induced a slight change in acetylcholinesterase activity. The results of the present study suggest that C. trifoliatum extract can be used as an insecticide to manage N. lugens populations.

The dried twigs of Piper ribesioides were used to prepare various extracts in different solvents. Each extract was evaluated for their toxicity against 2nd instar larvae of Spodoptera exigua. The highest acute toxicity was observed for ethyl acetate extract with an LD50 of 3.25 and 2.50 μg/larva and LD90 of 9.19 and 8.15 μg/larva after 24 and 48 h post-treatment after topical application. Piperine, methyl piperate, N-cinnamoyl-(2-phenylethyl) amine, pinostrobin, pinocembrin, cinnamic acid, lemairamin, N,N-Diphenylcinnamide, and methyl cinnamate were isolated from this extract that was toxic to S. exigua larvae. Cinnamic acid was the most active compound with a LD50 of 0.17 μg/larva after 48 h of topical treatment. Piperine was significantly similar in activity (LD50 = 0.19 μg/larva), but toxicity decreased with the change in structural configuration as observed with methyl piperate (LD50 = 0.73 μg/larva). Other compounds were 3 to 11-fold less toxic than cinnamic acid and piperine. Growth of survived S. exigua larvae until adult emergence after topical application was recorded and maximum inhibition of about 70% was observed after the application of cinnamic acid. Egg hatch was only 29.11% after cinnamic acid treatment, compared to 97.38% in controls. Neither induction nor inhibition of detoxification enzymes due to treatment of extracts were statistically significant, however, individual compounds like cinnamic acid, methyl cinnamate, piperine, pinostrobin, pinocembrin, and lemairamin did show a moderate impact on these enzymes.

BackgroundSpodoptera exigua Hübner (Lepidoptera: Noctuidae) is a widely occurring insect pest of several crops conventionally controlled by pyrethroids and organophosphates hazardous for the environment and human health. Thus, the alternatives are biocide-based phytochemicals. Accordingly, the Piper ribesioides Wall. (Piperales: Piperaceae) plant, well distributed in the northern regions of Thailand (Nan Province), was used due to its known bioactivity against insects. The objective was to determine the feeding deterrent activity of P. ribesioides extracts and isolated allelochemicals under laboratory conditions and correlate the efficacy under greenhouse conditions after the extracts were applied to S. exigua larvae infesting potted Brassica oleracea var. alboglabra (Bailey) Musil plants. Another objective was to look at the impact of spray applications on detoxification enzymes to check the possibility of resistance development against such natural extracts.ResultsEthyl acetate extract deterred feeding of larvae better than other extracts with the concentrations causing 50% feeding inhibition (FI50) of 26.25 µg/cm2 and feeding deterrence index (FDI) of 91.8%, which was slightly lower than the positive control (cypermethrin, FDI = 100%; FI50 0.027 µg/cm2). The most effective feeding deterrent compounds against S. exigua were pinostrobin and pinocembrin with FDI range of 77 to 90% and FI50 values of 14.39 and 19.38 µg/cm2. In the greenhouse, the larvae treated on potted B. oleracea at FI50 concentrations (determined in laboratory experiments), ethyl acetate extract gave the highest mortality of 63.33% within 24 h of first spray and total of 73.33% after 24 h of the second spray. Impact on detoxification enzymes (24 h post-treatment) was determined from survived 3rd instars of S. exigua using spray applications. Inhibition of carboxylesterase (CE) was 1.94-fold after hexane extract treatment. However, ethyl acetate extract inhibited glutathione-s-transferase (GST) 1.30-fold.ConclusionsEthyl acetate extract of P. ribesioides twigs and isolated pinostrobin and pinocembrin compounds were potential antifeedants against S. exigua larvae. The data obtained also showed that such antifeedant levels of treatment could be used in greenhouse or field trials directly as an extract after establishing the efficacy of extracts and the active compounds therein under laboratory conditions.

Spodoptera litura Fabricius (Lepidoptera: Noctuidae) is one of the most destructive pests of various crops cultivated in Thailand. Spodoptera litura larvae, at early stages, attack the leaves and feed on every part of infested crops in later stages. Acorus calamus essential 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. litura larvae. Methanol extract of A. calamus, chrysin, and 4-hydroxy acetophenone compounds were the most effective feeding deterrents with FD50 of 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. calamus methanol 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. calamus was 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

Spodoptera litura Fabricius (Lepidoptera: Noctuidae) is one of the most destructive pests of various crops cultivated in Thailand. Spodoptera litura larvae, at early stages, attack the leaves and feed on every part of infested crops in later stages. Acorus calamus essential 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. litura larvae. Methanol extract of A. calamus, chrysin, and 4-hydroxy acetophenone compounds were the most effective feeding deterrents with F[D.sub.50] of 87.18, 10.33, and 70.77 [micro]g/[cm.sup.2], 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. calamus methanol 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. calamus was 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. Key words: Acorus calamus, chrysin, 4-hydroxy acetophenone, feeding deterrent, Spodoptera litura