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Antifeedant, growth regulatory and biochemical effects of terpenes and phenylpropenes on Spodoptera littoralis Boisduval

Abdelgaleil, Samir A. M., Abou-Taleb, Hamdy K., Al-Nagar, Nagwa M. A., Shawir, Mohamed S.
International journal of tropical insect science 2020 v.40 no.2 pp. 423-433
Spodoptera littoralis, alpha-amylase, antifeedants, antifeeding activity, biopesticides, cineole, enzyme activity, enzyme inhibitors, eugenol, exposure duration, farnesol, growth inhibitors, growth retardation, inhibitory concentration 50, insect larvae, insecticidal properties, insecticides, instars, larval development, mortality, pests, proteinases, screening, secondary metabolites, sesquiterpenoids, toxicity
Screening the biological activities of plant secondary metabolites on economic pests can lead to discovery new ecofriendly biopesticides. The aim of this work was to evaluate the antifeedant, growth inhibitory and toxic activities of seven monoterpenes, two phenylpropenes and two sesquiterpenes on 2nd larval instar of Spodoptera littoralis. The tested compounds induced a significant antifeedant effect at various concentrations (500, 1000 and 2000 mg/kg), particularly after 6 and 9 days of exposure. Among the tested compounds, trans-cinnamaldehyde, α-terpinene, (−)-citronellal and 1,8-cineole were the most potent antifeedants after the three exposure periods. In general the tested compounds showed remarkable antifeedant activity after 9 days of exposure as their antifeedant indices ranged between 44.0 and 80.1%. On the other hand, the tested compounds drastically inhibited the growth of S. littoralis larvae at the tested concentrations. The larval growth inhibition ranged between 21.4 and 100% with cuminaldehyde, 1,8-cineole and eugenol being the most potent growth inhibitors. Some of the tested compounds caused significantly higher antifeedant and growth inhibitory effects than a reference insecticide, pyriproxifen. In general, the tested compounds showed higher growth inhibition than antifeedant effect. The tested compound also induced S. littoralis larval morality which improved with increasing exposure time and concentration. Cuminaldehyde, 1,8-cineole and (−)-carvone showed highest toxicity with 100.0, 97.0 and 77.0% mortality, respectively, at 2000 mg/kg after 9 days of exposure. Biochemical studies revealed that trans-cinnamaldehyde (IC₅₀ = 0.03 mM), farnesol (IC₅₀ = 0.04 mM) and eugenol (IC₅₀ = 0.06 mM) are potent α-amylase inhibitors. These three compounds also caused significant inhibition of total proteases activity. This is the first report on antifeedant, growth inhibitory and insecticidal activities of the tested compounds on S. littoralis. Moreover, the strong bioactivity reported in this study indicated that these compounds have a potential to be used as bioinsecticides.