Chemical Composition, Fumigant and Contact Toxicities of Essential Oils Isolated from Egyptian Plants Against the Stored Grain Insects; Sitophilus oryzae L. and Tribolium castaneum (Herbst)

Essential oils from twenty Egyptian plants belong to 8 different families, namely, Artemisia judaica, A. monosperma, Astoma seselifolium, Callistemon viminals, Citrus aurantifolia, C. lemon, C. paradisi, C. sinensis, Cupressus macrocarpa, C. sempervirens, Myrtus communis, Origanum vulgare, Pelargonium graveolens, Pituranthos tortuosus, Rosmarinus officinalis, Syzygium cumini, Schinus mope, S. terebinthifolius, Thuja occidentalis and Vitex agnus-castus, were isolated by hydro-distillation. Chemical composition of the isolated oils was identified by gas chromatograph/mass spectrometer (GC/MS). The isolated oils were enriched with monoterpene hydrocarbons (i.e., limonene, sabinene, beta-pinene, gamma-terpinene, alpha-phellandrene, beta-phellandrene, delta-3-carene, cis-ocimene) and oxygenated monoterpenes (i.e., terpinen-4-ol, beta-thujone, 4-terpineol, linalool, alpha-citral, beta-citronellol, 1, 8-cineole, camphor, pulegone, alpha-terpinolene). However, the oil of S. terebinthifolius was enriched with sesquiterpenes and the oil of V. agnus-castus was contained similar quantities of monoterpenes and sesquiterpenes. Fumigant and contact toxicities of the essential oils were evaluated against two stored grain insects; Sitophilus otyzae L. and Tribolium castaneum (Herbst). In fumigation assay, the oil of O. vulgare (LC50 = 1.64 mg/l air) exhibited highest toxicity to S. oryzae. In addition, the oils of C. lemon (LC50 = 9.89 mg/l air), C. viminals (LC50 = 16.17 mg/l air), C. sempervirens (LC50 = 17.16 mg/lair) and C. sinensis (LC50 = 19.65 mg/l air) showed remarkable fumigant toxicity against this insect. On the other hand, the oil of O. vulgare (LC50 = 9.97 mg/l air) displayed highest fumigant toxicity to adults of T. castaneum. In addition, the oils of C. viminals, C. sinensis, C. lemon, M. communis and S. terebinthifolius exhibited strong fumigant toxicity with LC50 values less than 30 mg/l air. In contact assay, the oils of A. judaica, C. viminals and O. vulgare caused highest toxicity to S. otyzae with LC50 values of 0.08, 0.09 and 0.11 mg/cm(2), respectively. In case of T. castaneum, the oils of A. monosperma (LC50 = 0.07 mg/cm(2)) and O. vulgare (LC50 = 0.07 mg/cm(2)) were the most potent toxicants, followed by C. macrocarpa, C. aurantifolia, R. officinalis and A. seselifolium. The results of this study indicated that some of the tested essential oils had potent fumigant and contact toxicities against S. oryzae and T. castaneum. Therefore, these oils have the potential to be developed as new green insecticides and/or fumigants for managing both insects, particularly in storage sites.