The Combined Effect of Gamma Radiation and Fenugreek Oil for the Control of the Cowpea Weevil Callosobruchus maculatus (F.) (Coleoptera: Bruchidae)1

Abstract

Damage caused by the cowpea weevil Callosobruchus maculatus (F.) is the major constraint to cowpea grain production in most cowpea producing countries. The activity of fenugreek essential oil was evaluated against the one-week-old adults of C. maculatus which exhibited good activity with an LC50 value of 195.44 ppm. Two gamma radiation doses were chosen (50 and 100Gy) to study their combined effects with the LC75, LC50, LC25 and LC10 values of fenugreek essential oil on the mortality of C. maculatus adults. The weevils were subjected to gamma radiation then exposed to vapors of the volatile oils and mortality was recorded daily for four days. It was observed that mortality increased as a result of the combined effect of the two agents. Mortality percentages were 93.33, 81.66, 68.33, and 51.66% when one-week-old adults of C. maculatus were irradiated with 100Gy and exposed to LC75, LC50, LC25 and LC10 values of fenugreek essential oil, respectively, 96 h post-treatment. The irradiated weevils with 50Gy showed 85, 71, 60, and 45% mortality, respectively, 96 h post-treatment. The integration of fenugreek essential oil and gamma radiation is a safe, effective and affordable control method against cowpea weevils and they are promising to be the main components of Integrated Pest Management (IPM) programs of this weevil.