Environmental and health concerns of synthetic insecticides highlight the need for new strategies to protect stored grains insect infestation in Egypt. The contact and fumigant toxicity of three local Egyptian essential oils; geranium, Pelargonium graveolens Herb, basil, Ocimum basilicum Herb, and fennel, Foeniculum vulgare seeds to adults of Sitophilus oryzae (Coleoptera: Curculionidae) and Callosobruchus macullatus (Coleoptera: Bruchidae) were investigated. Three different methods of oil applications were adopted; thin film residue (without grains), mixing with grains, and fumigation. It was observed that, in the absence of rice grains, geranium oil was the most effective against S. oryzae and C. maculatus with lower LC50 of 710, and 705 ppm, respectively 3 days post exposure, followed by both basil and fennel oils (1305 & 3848 ppm/ 3 days, and 3030 & 1548 ppm/ 3 days), respectively. In the presence of grains, mixing of the same oil concentrations with grains required longer time and higher concentration of oils to achieved 100% mortality of S. oryzae and C. maculates adults. However, for S. oryzae adults only fennel oil exhibited the lowest LC50 (10956 ppm/ 6 days) followed by basil oil (20 ppm/ 6 days). Geranium oil evoked no detectable mortality of S. oryzae adults. Fennel oil induced the highest mortality rate to C. maculates (125 ppm/ 5 days) followed by geranium, and basil oils (485.61 and 2641.43 ppm, respectively). In fumigation bioassay, basil oil achieved the lowest LC50 of 1175 ppm/ 3 days post exposure of S. oryzae, followed by geranium, and fennel oils (28675 ppm and 18496 ppm/ 3 days post exposure, respectively). In the case of C. maculatus, geranium oil induced the lowest LC50 (21492 ppm/ 3 days) followed by basil (35009 ppm/ 3 days) and fennel oils (50681 ppm/ 3 days). Data were discussed in the light of oil's toxicity and susceptibility of the two weevil species. The results strongly suggest the possibility of using essential oils as toxicant and fumigant against S. oryzae and C. maculates adults in storage facilities in Egypt.
Essential oils, rice, rice weevil Sitophilus oryzae, C. maculates, cowpea, toxicity, fumigant