Phytochemical and Insecticidal Activity of Some Thyme Plants' Essential Oils Against Cryptoblabes gnidiella and...

Mango fruits are one of the strategic fruit crops in different countries that are attacked by several serious pests such as Cryptoblabes gnidiella and Scirtothrips mangiferae. Natural extracts, especially essential oils, provide several promising insecticide agents to control different insects as an alternative to synthetic insecticides. Using Clevenger-type hydrodistillation, the essential oils of five thyme plants-Thymus vulgaris, Origanum vulgare, Thymus argenteus, Thymus citriodorus, and Origanum syriacum-from Saudi Arabia and Egypt were extracted, and GC/MS analysis was performed. In addition, some chemical parameters of the five species were determined, such as chlorophyll a, chlorophyll b, β-carotene, total antioxidant capacity, total phenols, and total flavonoids. Two compounds, thymol and carvacrol, were identified in T. vulgaris and O. vulgare at ratios of 69.45 and 64.82%, respectively. These major compounds were isolated and identified using ¹H NMR analysis. The insecticidal potentials of the five essential oils and their pure isolated compounds were evaluated on C. gnidiella and S. mangiferae on mango inflorescences. The results showed that T. vulgaris and O. vulgare oils were the most potent against C. gnidiella (LC₅₀, 183.33 and 164.68 ppm, respectively) and S. mangiferae (18.93 and 16.93 ppm, respectively). Thymol and carvacrol had the highest effect on both insects. Furthermore, the effect of thymol and carvacrol at LC₅₀ values on some biochemical parameters of C. gnidiella was determined. Therefore, thymol and carvacrol from Thymus species are promising compounds that could be used as insecticides against the harmful insects C. gnidiella and S. mangiferae on mango inflorescences.