Insecticidal Activity of Essential Oils in Cylas formicarius (Fabricius) (Coleoptera: Brentidae)

The sweet potato weevil, Cylas formicarius (Fabricus), is one of the most destructive and widely distributed pests affecting sweet potato, Ipomoea batatas (L.) Lam. It has a high reproductive capacity, a short generation time, and is difficult to control due to its soil-dwelling nature. Currently, the control strategy against C. formicarius relies mainly on treatment with synthetic insecticides. Considering that this pest causes the greatest damage during the harvest and post-harvest period on stored plants, control using chemical products is not recommended due to the increased risk of high levels of pesticide residues in the roots. In order to reduce the use of insecticides, there is a need to develop an environmentally safer control method, such as alternative solutions that can rely on the use of essential oils (EOs), which can be used in both conventional and organic production systems. Seven essential oils, namely Thymus Gobicus, garlic oil (Allium sativum), pure yellow marigold oil (Calendula officinalis), eucalyptus, mustard seed oil, peppermint, and rosemary, were used to evaluate the mortality of adults, second- and third-instar larvae and pupae. The applied EOs were dissolved in acetone in three different concentrations, 1%, 5%, and 10%. The best results were obtained in the larval and pupal stages with peppermint oil standing out as the most effective, presenting the highest mortality values ​​in the second and third instar, especially at concentrations of 10% and, to a lesser extent, 5%. Peppermint, eucalyptus, thyme and rosemary oils were the most effective oils in the mortality of newly pulped pupae, especially at concentrations of 10%. Both controls presented low mortality values ​​in relation to the treatments with oils, indicating that mortality is significantly lower without the application of the oils.