Laboratory Evaluation of Contact and Feeding Deterrent Effects of Selected Essential Oils Against Different Life Stages of Cylas formicarius (Coleoptera: Brentidae)

The sweet potato weevil, Cylas formicarius (Fabricius) (Coleoptera: Brentidae), is one of the most destructive pests of sweet potato [Ipomoea batatas (L.) Lam.] crops worldwide. Current management of the sweet potato weevil relies heavily on conventional pesticides, raising concerns about pesticide residues, environmental impacts, and the development of pesticide resistance. This study evaluated the effects of seven essential oils (EOs): eucalyptus (Eucalyptus globulus), garlic (Allium sativum), marigold (Calendula officinalis), mustard seed (Sinapis alba), peppermint (Mentha piperita), rosemary (Rosmarinus officinalis), and thyme (Thymus gobicus) against different life stages of C. formicarius under laboratory conditions. Feeding activity, oviposition, larval mortality, pupal mortality, and adult survival were evaluated using EO concentrations of 1%, 5%, and 10%, with acetone and distilled water as control treatments. Each treatment consisted of six replicates, with 10 insects per replicate. Statistical analyses were performed using logistic regression models with a binomial distribution. Significant effects of oil type and concentration were observed as lethal to weevil larval and pupal stages. Similarly, the feeding and oviposition were significantly impacted (p < 0.0001). Peppermint oil exhibited the highest efficacy, causing complete or near-complete mortality of second- and third-instar larvae and pupae at 10%. This also substantially reduced adult survival, feeding activity, and oviposition. Rosemary, thyme, and eucalyptus, at higher concentrations. Most oils almost completely suppressed oviposition. These findings demonstrate that plant-derived essential oils (EOs) exhibit significant insecticidal activity against Cylas formicarius, indicating their promise as sustainable tools for integrated pest management programs in sweet potato production systems.