Abstract:Objective: A study was conducted to evaluate the effect of two essential oils (Chenopodium and Thymus) and of microbial agent (Beauveria bassiana) and their combinations against cowpea bruchid, Callosobruchus maculatus. Methods: In choice test, Thymus and Chenopodium oils revealed a strong repellent activity against Callosobruchus maculatus. Accumulative mortality of beetles increased gradually with the increase of exposure intervals. Chenopodium oil treatment gave the highest mortality percentage of 76% after 168 h from treatment followed by Thymus oil treatment which amounted to 63%. Chenopodium oil was the most effective in enhancing the potency of Beauveria bassiana and decreased LC50 of the target insect. The effect of formulated Chenopodium oil with Beauveria bassiana fungi displayed several different modes of action, by reducing oviposition and adult emergence (F1) of Callosobruchus maculatus. Results: The oviposition was completely inhibited when the seeds were treated with Chenopodium oil + Beauveria bassiana during 20, 40 and 60 days of storage suppressing Callosobruchus maculatus infestation during storage.