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BACKGROUND Thymol, a natural phenolic monoterpene originating from Thymus vulgaris, is recognized as a safe and potent botanical insecticide to many insects. The structural modification of thymol into thymyl esters is a potential approach for the development of novel insecticides, which showed more toxicity than thymol. However, there are no reports on the insecticidal activity of thymyl esters to control Spodoptera litura. RESULTS Thymol was structurally modified into ten thymyl esters by esterification using a new reagent, PPh3/Br3CSO2Ph. The insecticidal activity of these compounds was examined against the second instars of Spodoptera litura using a topical application. Among the ten thymyl esters evaluated, thymyl cinnamate was the most toxic with LD50 = 0.41 and 0.34 μg/larva after 24 and 48 h posttreatment, respectively. In addition, thymyl cinnamate‐treated larvae showed increasing carboxylesterase and acetylcholinesterase activities in vivo experiment, whereas glutathione S‐transferase activity showed no significant difference. CONCLUSION Thymyl cinnamate were first reported to exhibit toxicity against S. litura 2.41–2.46 fold more efficient than thymol. However, the detailed biochemical interactions are necessary for further development of novel insecticides. © 2019 Society of Chemical Industry

Background: Spodoptera litura larvae are polyphagous insects that have become a significant pest in recent years. The spread of this pest has led to the continuous usage of insecticides on crops. Some plant extracts have been used as a mixture to control insect pests and improve productivity. Methods: A plant-based mixture was mixed at a ratio of 1:1 v/v to demonstrate the effect on contact toxicity, feeding (no-choice test), and enzyme activities on S. litura. The active compounds of P. retrofractum and A. calamus were isolated by preparative thin-layer chromatography (PTLC). Results: Our results showed that binary mixtures from P. retrofractum and A. calamus exhibit the highest contact toxicity and antifeedant activity at a 1:1 ratio of LD 30 :LD 10 dose (3.213 µg/larva P. retrofractum + 3.294 µg/larva A. calamus). The main active ingredient from each crude extract was (2E,4E,14Z)-N-isobutylicosa-2,4,14-trienamide from P. retrofractum, and beta-asarone and alpha-asarone from A. calamus. Additionally, A. calamus seems to be the synergistic compound. Some compound mixtures increased the glutathione-S-transferase activities in vivo; whereas, almost no significant differences in esterase activities were noted. Conclusion: The results indicated that the ethanolic crude extracts of P. retrofractum and A. calamus mixtures could be used as the pesticidal compound and to develop a binary mixture formulation for controlling lepidopteran pests. However, the toxicity of this mixture to mammals needed to be explored before commercial development.

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Essential oils are well known to act as biopesticides. This research evaluated the acute toxicity and synergistic effect of essential oil compounds in combination with cypermethrin against Spodoptera litura Fabricius (Lepidoptera: Noctuidae). The effects of distillation extracts of essential oils from Alpinia galanga Zingiberaceae (Zingiberales) rhizomes and Ocimum basilicum Lamiaceae (Lamiales) leaves; one of their primary essential oil compounds 1,8-cineole; and linalool were studied on second-instar S. litura by topical application under laboratory conditions. The results showed that A. galanga had the highest control efficiency, whereas1,8-cineole provided a moderate efficacy. The mixtures of linalool, 1,8-cineole, O. basilicum, or A. galanga with cypermethrin were synergistic on mortality. Activity measurements of the main detoxification enzymes show that linalool and 1,8-cineole inhibit the activity of cytochromes P450 and carboxylesterases, which could explain their synergistic effect. Based on our results, the use of these mixtures represents an ideal eco-friendly approach, helping to manage cypermethrin resistance of S. litura.

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Sixteen N-phenylphthalimide derivatives were synthesized and their ability to inhibit alpha-glucosidase was investigated. N-(2,4-dinitrophenyl)phthalimide was a potent inhibitor of yeast alpha-glucosidase (IC50; 0.158 +/- 0.005 mM) and maltase (IC50; 0.051 +/- 0.008 mM), whereas it did not inhibit sucrase. From a Lineweaver-Burk plot of alpha-glucosidase kinetics, N-(2,4-dichlorophenyl)phthalimide was found to be a competitive inhibitor of yeast alpha-glucosidase. These results indicate that N-(2,4-dinitrophenyl)phthalimide could be a representative of a new group of alpha-glucosidase inhibitors.

The beet armyworm (Spodoptera exigua (Hübner)) is one of the most important vegetable pests in Thailand. After 24 hr of both dipping and sprayer bioassay, estimation of LC 50 of the ethyl acetate extract of Jatropha gossypifolia senescent leaves demonstrated toxicity to secondary instar S. exigua larvae because in this stage most armyworm start to move to other plants and it is also the first susceptible stage for toxicity tests. Ricinine, the main alkaloid separated from ethyl acetate crude extract, showed toxicity on secondary instar larvae by the sprayer method with an LC 50 of 3,215 ppm whereas the LC 50 value for ethyl acetate crude extract is 8,644 ppm. Thus, the ethyl acetate crude extract of Jatropha gossypifolia senescent leaves may have ricinine as the active ingredient and may be used as an alternative choice for the minimal application of chemical insecticides for Spodoptera exigua.