Investigation of bio-insecticidal activity of two aromatic essential oils against Tribolium castaneum (Herbst) (Coleoptera, Tenebrionidae)

Excessive application of synthetic insecticides damages not only the environment and agriculture, but also affects the human health. In this study we investigated greener methods to control an insect pest of stored products. We focalized our work on the characterization and study of the biological activity of Thymus algeriensis Boiss. and Reut (1852) and Thymus capitatus (L.) Hoffmanns. et Link (1809) essential oils against Tribolium castaneum Herbest (1797). The essential oils were obtained by hydrodistillation, analysed by GC/MS and screened for their insecticidal activity against T. castaneum using fumigation [1], topical application [2], repulsion [3], and feeding tests [4] at the doses of 1, 10 and 20%. The chemical analysis of the essential oils of these two species showed a qualitative and quantitative similarity. Indeed, they were both particularly rich in oxygenated monoterpenes (T. capitatus 85.1% and T. algeriensis 74.0%). The investigation of the bio-insecticidal activity of the essential oils by topical application showed that T. capitatus essential oil was more toxic against adults and nymphs (respectively 61% and 100% at the dose of 10%) than T. algeriensis. However, T. algeriensis was characterized by a higher repulsive activity (Class V at all the doses) and without any fumigant toxicity against T. castaneum adults. The study of the nutritional indices highlights a phagostimulant effect for T. capitatus and T. algeriensis oils. Even if quite similar, these different modes of action can be attributed to the different qualiquantitative composition of these two essential oils. More investigations, in particular about the mechanism of action, are needed in the aim of their possible future agronomic use in insect control to protect the environment and the living beings from insect pests.