| Summary: | <i>Plutella xylostella</i> L. is one of the world’s major pests of cruciferous crops. The indiscriminate use of synthetic insecticides has led to insecticide resistance and resurgence, and has been harmful to non-target organisms and the environment. Botanical insecticides are the best alternatives to synthetic pesticides for the management of pests in organic agriculture and integrated management. <i>T. sebifera</i> is an invasive species and has good potential as an insecticide due to the availability of plant material in some parts of India. The antifeedant activities of <i>T. sebifera</i> have not been reported against <i>P. xylostella</i> and other lepidopteron insects to date. Therefore, the current study targeted the characterization of leaf and bark extracts, feeding deterrence, synergistic and detoxification enzyme activities of leaf/bark ethanolic extracts/fractions, seed oil, and isolated compounds. UHPLC-QTOF-IMS analysis showed that shikimic acid, xanthoxylin, quercetin, kaempferol, methyl gallate, and stigmasterol are common metabolites identified in leaf and bark extracts. The combination of seed oil with bark extract showed higher deterrence (DC<sub>50</sub> = 317.10 mg/L) as compared to leaf/bark extracts alone. Gallic acid showed higher deterrence (67.48%) than kaempferol and quercetin. The <i>n</i>-butanol fraction of bark was more repellent (RC<sub>50</sub> = 414.61 mg/L). Based on DC<sub>50</sub>, the seed oil with leaf extract (1:1 ratio) alone with choice and seed oil with leaf and bark extract without choice showed synergistic interaction, but seed oil with bark extract with choice showed additive interaction. The ethanol extract of leaf, bark, and seed oil inhibited GST and AChE in <i>P. xylostella.</i> The leaf extract and seed oil or their combinations may be recommended as antifeedants to reduce damage by <i>P. xylostella</i> based on persistence, antifeedant, phytotoxicity, safety to predators/parasitoids, etc., under field conditions.
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