Toxicity and Feeding Deterrence Activity of Mentha×piperita and Baccharis milleflora Essential Oils on Microtheca ochroloma (Coleoptera: Chrysomelidae)

Abstract

Abstract This study evaluated the bioactivity of Mentha×piperita L. (Lamiaceae) and Baccharis milleflora Less. (DC.) (Asteraceae) essential oils (EOs) against the yellowmargined leaf beetle Microtheca ochroloma Stål, 1860 (Coleoptera: Chrysomelidae), under laboratory conditions. Different EOs concentrations were tested on adults and larvae for toxicity, through topical application, and for feeding deterrence, using treated Chinese cabbage cut leaves. M. piperita EO showed higher toxicity to adults (LC₅₀ = 0.06%) than to larvae (LC₅₀ = 1.33%) and reduced the foliar consumption to 7.76% in adults and 10.93% in larvae at EO concentrations of 0.10% and 0.15%, respectively. The EO of B. milleflora showed relatively lower toxicity (LC₅₀ = 1.12% to adults and 1.67% to larvae) but a stronger feeding deterrence effect, with foliar consumption reduced to 0% in adults and 0.09% in larvae at a 1% EO concentration. However, higher EOs concentrations (0.3% and 2% of M. piperita and B. milleflora, respectively) caused phytotoxic effects on leaves, emphasizing the need for carefully managed dosages to prevent crop damage. This study is the first to test EOs against M. ochroloma and the first to evaluate B. milleflora EO on a defoliating beetle, highlighting their potential as innovative biopesticides with effective toxicity and feeding deterrence at low concentrations.