Ethanolic Botanical Extracts: A Bioinsecticide Approach to Controlling Epicauta atomaria (Coleoptera: Meloidae)

The blister beetle, Epicauta atomaria (Germar) (Coleoptera: Meloidae), is a Neotropical pest of various horticultural crops. This pest consume leaves causing significant reduction in the plant foliage. To develop sustainable tools for managing this insect species, we evaluated the repellent and insecticidal activity of ethanolic extracts from six plant species commonly found in Argentina: Artemisia annua (L.), Cantinoa mutabilis ((Rich.) Harley and J.F.B Pastore), Dysphania ambrosioides ((L.) Mosyakin and Clemants), Lantana camara (L.), Ricinus communis (L.), and Taraxacum officinale (F.H Wigg). The results showed that D. ambrosioides was the most active extract, with strong repellent activity at concentrations below 200 μg/μL (1.5 mg/cm²). Additionally, the extract caused a mortality rate of 78% at 10 μg/μL after 24 h, with an LC₅₀ of 7.9 μg/μL against E. atomaria. The enzymatic activity of E. atomaria acetylcholinesterase was evaluated in vitro to reveal the mode of action, resulting in a 58% inhibition at 5.0 μg/μL. The main bioactive compounds in fractionated D. ambrosioides ethanolic extracts were identified by GC-MS. The extract contained high concentrations of thymol and carvacrol in the less polar fractions, which were the most active. The bioactivity of both compounds against E. atomaria was also tested, showing strong insecticidal activity with an LC₅₀ of 1.6 and 1.4 μg/μL for thymol and carvacrol, respectively. Overall, our results highlight the potential of D. ambrosioides as a biopesticide for managing E. atomaria.