Evaluation of the Insecticidal and Repellent Potential of Cymbopogon schoenanthus L. (Spreng) Essential Oil and Azadirachta indica Seed Oil on Adults of Cletus ochraceus (Hemiptera: Coreidae), a Pest of Cashew Trees in Togo

Abstract

Cletus ochraceus is one of the most harmful pests affecting cashew trees in Togo. Currently, the only method of controlling this pest is through chemical control, which unfortunately has serious consequences for human health and the environment. In order to find an alternative to the use of synthetic chemical pesticides, the insecticidal and repellent properties of Cymbopogon schoenanthus essential oil and neem seed oil (Azadirachta indica) were evaluated on Cletus ochraceus adults in vitro by contact. After preliminary tests of each oil and their combination, five concentrations of these oils and their equivolume mixture were selected and prepared at a rate of four replicates per concentration. The insecticide tests were carried out by spraying the solutions directly onto the insects. The repellence test was carried out using the preferred area method on filter paper, followed by determination of the percentage of Cletus present in the treated area. Each of the extract concentrations was applied to half of a piece of blotting paper placed in a 9 cm diameter Petri dish on which 10 Cletus were placed. When applied by contact, the combination of C. schoenanthus and A. indica oils showed moderate toxic activity (LC₅₀ = 20.7 µl.ml⁻¹), proving to be more effective than neem oil alone (LC₅₀ = 40.5 µl.ml⁻¹), but less effective than C. schoenanthus essential oil (LC₅₀ = 11.6 µl.ml⁻¹). Repellency tests revealed a high repellent potential for C. schoenanthus, the combination of oils, and a low repellent potential for neem seed oil, with percentages of 87.5%, 68.6%, and 23%, respectively. C. schoenanthus essential oil could be used as an active ingredient in the formulation of a biopesticide, as an alternative to synthetic chemical insecticides.