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.

中文翻译：

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萜烯和苯丙烯对斜纹夜蛾 Boisduval 的拒食、生长调节和生化作用

筛选植物次生代谢物对经济害虫的生物活性可以发现新的生态友好型生物农药。这项工作的目的是评估七种单萜、两种苯丙烯和两种倍半萜对 Spodoptera littoralis 2 龄幼虫的拒食、生长抑制和毒性活性。测试化合物在不同浓度（500、1000 和 2000 毫克/千克）下引起显着的拒食效应，尤其是在暴露 6 天和 9 天后。在测试的化合物中，反式肉桂醛、α-萜品烯、(-)-香茅醛和 1,8-桉树脑是三个暴露期后最有效的拒食剂。一般而言，测试化合物在暴露 9 天后表现出显着的拒食活性，因为它们的拒食指数介于 44.0 和 80.1% 之间。另一方面，受试化合物在受试浓度下显着抑制了滨海沙门氏菌幼虫的生长。幼虫生长抑制范围在 21.4% 和 100% 之间，其中孜然醛、1,8-桉树脑和丁子香酚是最有效的生长抑制剂。与参考杀虫剂吡丙昔芬相比，一些测试化合物引起明显更高的拒食和生长抑制作用。一般而言，受试化合物显示出比拒食效应更高的生长抑制作用。受试化合物还诱导了S. littoralis 幼虫道德，其随着暴露时间和浓度的增加而改善。孜然醛、1,8-桉树脑和 (-)-香芹酮在 2000 mg/kg 暴露 9 天后表现出最高的毒性，死亡率分别为 100.0、97.0 和 77.0%。生化研究表明，反式肉桂醛 (IC50 = 0.03 mM)，法呢醇 (IC50 = 0.04 mM) 和丁香酚 (IC50 = 0.06 mM) 是有效的 α-淀粉酶抑制剂。这三种化合物也引起总蛋白酶活性的显着抑制。这是关于受试化合物对 S. littoralis 的拒食、生长抑制和杀虫活性的第一份报告。此外，本研究报告的强大生物活性表明这些化合物具有用作生物杀虫剂的潜力。