Bioactivity screening of plant ethanol extracts against Plutella xylostella and field evaluation of an optimized botanical combination formulation

Plutella xylostella is a major pest of cruciferous vegetables. The prolonged overuse of chemical insecticides has resulted in increased resistance in P. xylostella populations, highlighting the urgent need for environmentally friendly and effective alternative control strategies. In this study, ethanol extracts from 15 plant species collected from the Qinling Mountains of China were systematically evaluated for their insecticidal, antifeedant, and oviposition-repellent activities against P. xylostella. Laboratory bioassays were conducted using leaf-dipping and leaf-disc methods. Among the tested plants, ethanol extracts of Atropa belladonna and Blumea riparia var. megacephala exhibited the strongest biological activities. Specifically, A. belladonna extract achieved corrected mortality, antifeedant, and oviposition-repellent rates of 83.11%, 89.46%, and 78.57%, respectively, whereas B. riparia var. megacephala extract produced corrected mortality, antifeedant, and oviposition-repellent rates of 73.53%, 87.45%, and 82.14%, respectively. When combined at a volume ratio of 8:2, the two extracts showed enhanced insecticidal activity, with a median lethal concentration (LC50) of 65.762 mg/mL and a co-toxicity coefficient consistent with an additive effect without antagonism. A stable emulsifiable concentrate (EC) formulation was subsequently developed through optimization of the solvent and surfactant system. Field trials demonstrated that the 10% botanical EC effectively suppressed P. xylostella populations, achieving a control efficacy of 58.35% at 7 days post-application, which was comparable to that of the commonly used insecticide emamectin benzoate. Collectively, these findings suggest that A. belladonna and B. riparia var. megacephala have potential as botanical insecticide resources for the integrated management of P. xylostella and may contribute to more sustainable agricultural practices.