Variations of chemical composition of two Algerian essential oils collected for different seasons and assessment of their insecticidal toxicity against three moth pests

The aims of this work were to point out the seasonal variation in chemical composition and evaluate the insecticidal activities of Mentha spicata and Thymus vulgaris essential oils against larvae of three moths Ectomyelois ceratoniae, Ephestia kuehniella and Plodia interpunctella. GC-MS analyses indicated that major components of M. spicata essential oil were carvone, 1, 8-cineole and limonene. However, linalool, camphor and gamma-terpinene were the main compounds for T. vulgaris. Results showed that chemical composition varied with plant species, as well as seasons. On the other hand, results indicated that mortality percentages were highest during the summer season at the concentration 16 mu l/l air. Thus, fumigant toxicity depends on insect species, plants, seasons and concentrations. Besides, E. kuehniella was more sensitive to both oils as compared to E. ceratoniae and P. interpunctella. The LC50 values were 0.29, 4.40 and 2.51 mu l/l air, respectively, for M. spicata. Concerning T. vulgaris, the respective LC50 values were 0.062, 4.61 and 3.23 mu l/l air for E. kuehniella, E. ceratoniae and P. interpunctella. Furthermore, for the most toxic season, LT50 values of M. spicata were 0.7, 5.2 and 3.2 days, respectively, for E. kuehniella, E. ceratoniae and P. interpunctella. Regarding T. vulgaris, LT50 values were 0.35, 6.5 and 4.58 days, respectively, for E. kuehniella, E. ceratoniae and P. interpunctella. Therefore, essential oils collected during summer season could be considered as an effective tool of control against moths of stored products.