Selected essential oils against Cylas formicarius (Coleoptera: Brentidae) under laboratory conditions

The sweet potato weevil (SPW), Cylas formicarius (Coleoptera: Brentidae), is a serious pest of sweet potato (Ipomoea batatas) in the United States and around the world. The current management practices rely heavily on synthetic insecticides, which may lead to pesticide residues in the tubers and non-target effects on the natural enemies. Essential oils (EOs) are considered promising alternatives due to their natural origin, low environmental impact, and specific biological activities, including insecticidal, repellent, oviposition deterrent, antifeedant, and growth and reproductive inhibitor properties. This study evaluated seven EOs: Eucalyptus globulus, Allium sativum, Calendula officinalis, Brassica juncea, Mentha piperita, Rosmarinus officinalis, Thymus gobicus at concentrations of 1%, 5%, and 10%, along with two controls (water and acetone) treatments and three replicates under laboratory conditions [temperature (25±5°C), relative humidity (65±5%), and a photophase of 14L:10D]. All EOs treatments reduced feeding in C. formicarius, showing repellent and/or deterrent effects. The females of SPW caused more perforations than the males. Mortality rates among larvae (2nd and 3rd instars) and pupae varied, with peppermint found to be the most effective across all concentrations (1%, 5%, and 10%) tested. Adult mortality was observed to increase proportionally to the concentration of the oils. The most effective essential oils at 10% concentration were peppermint (100%), thyme (100%), eucalyptus (98%), and rosemary (above 95%), showing strong larval and pupal mortality. Further testing of the peppermint, rosemary, and thyme under the open field conditions is necessary to provide recommendations of these potential EOs for the IPM to sustain sweet potato production.