Contact toxicity of essential oils (EOs) isolated from cumin, Cuminum cyminum seeds, marigold, Tagetes terniflora leaves and flowers, mandarin, Citrus reticulata and bitter orange, Citrus aurantium, fruit peels and monoterpenoids, citrenallol, geraniol and linalool against Sitophilus oryzaeLinnaeus and Callosobruchus maculatus Fabricius adults were evaluated. A synthetic pyrethroid, Deltamethrin, was employed as a standard. All EOs grain-protective properties were concentration, time and insect species dependent. Two days post exposure, mandarin EO was the most toxic to S. oryzae with LC50 value of 8974 ppm, bitter orange and cumin EOs were the most toxic to C. maculatus with LC50 values of 1138.5 and 1626.2 ppm. Five days post exposure, bitter orange, mandarin, cumin, and marigold EOs showed similar contact toxic activities against S. oryzae with LC50 values of 1752.7, 2090.8, 2210.9, and 3296.6 ppm, respectively. Mandarin and cumin EOs were the most toxic against C. maculatus with LC50 values of 14 and 63 ppm, respectively. Deltamethrin was significantly most toxic agent than all tested EOs against both S. oryzae and C. macultatus with LC50 values of 10.7 and 8.7 ppm. Binary mixtures of all EOs were highly toxic against S. oryzae compared to the single EO. They possess either antagonistic or synergistic toxic effects against C. maculatus. All monoterpenoids showed a moderate contact toxic effect against both S. oryzae and C. maculatus adults compared with EOs.The results proved that EOs alone or in mixtures and monoterpenoids have the potentials to act as grain protectants against S. oryzae and C. maculatus.
Cumin, Marigold, Mandarin, Bitter orange, Citrenallol, Geraniol, Linalool, Deltamethrin