Comparative evaluation of insecticidal properties of essential oils of some selected botanicals as bio-pesticides against Cowpea bruchid, Callosobruchus maculatus (Fabricius) [Coleoptera: Chrysomelidae]

Abstract

Abstract Background The insecticidal activities of essential oils from seeds of five botanicals Tetrapleura tetraptera, Annona muricata, and Aframomum melegueta and leaves of Eucalyptus globulus and Ficus exasperata were evaluated as biopesticides against the storage pest of cowpea Callosobruchus maculatus (Fabricius). The oils were applied at the concentration of 1 ml/kg, 3 ml/kg, and 5 ml/kg of cowpea seeds mixed evenly. The experiment was laid out in a completely randomized design. The parameters assessed include the percentage of mortality, oviposition, adult emergence, seeds damaged, weight loss, and germinability capacity of the protected seeds. Results The results from the study showed that the effectiveness of the essential oils was dependent on application rates and time of exposure. In the treated cowpea seeds, A. melegueta essential oil was the most effective with 50% lethal concentration (LC50) value of 2.42 ml/kg and 95% lethal concentration (LC95) value of 4.86 ml/kg when compared to the other treatments as indicated by the application rate which caused 50% and 95% mortality of cowpea beetles. A. melegueta essential oil at the concentration of 5 ml/kg achieved 100% mortality of C. maculatus at 48 h of application. Cowpea seeds treated with 5 ml/kg of E. globulus essential oil significantly reduced (P 0.05) adverse effect on seed germination after 120 days of storage. Conclusion Based on the findings of this study, the essential oils could be explored as an alternative bio-pesticide to synthetic insecticide in the protection of stored cowpea against C. maculatus.

Keywords

• Botanicals
• Essential oils
• Callosobruchus maculatus
• Mortality
• Adult emergence