Essential oils of fennel, Foeniculum vulgare, geranium, Pelargonium graveolens, and basil, Ocimum basilicum were evaluated for their repellency, residual activity and detrimental effect on progeny production of Sitophilus oryzae and Callosobruchus maculatus. In dual and multi-choice assays, all applied oils significantly repelled the tested insects away of treated grains towards the control, whereas, the repellency of the tested oils was proportional to their concentration. Feeding adults of S. oryzae on rice grains and C. maculatus on cowpea grains treated with gradient concentrations of the tested oils reduced the net percentage of their newly emerged F1 progeny. The reduction of the new offspring of S. oryzae and C. maculatus was proportional to the concentration of the tested oils. Storage of rice or cowpea grains mixed with (LC50) of the fennel oil for various periods of time before weevils' exposure showed that mortality rates of S. oryzae and/or C. maculatus adults were higher after 1, 2, and 4 weeks of treatment than those after 2 and 3-months post storage. Data has been discussed in the view of the bioactivity of essential oils and their potential application in controlling stored grain pests.
Key words: Stored grain pests, Biology, Repellency, Persistence
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