Novel application of Trichilia Heudelotii planch: effectiveness of different polarity of organic solvents of leaf and stem bark extracts on the control of cowpea beetle

Abstract

Callosobruchus maculatus (cowpea beetle) is a field-to-store pest causing over 90% losses of cowpea. The search for new plant-derived crop protectant that can be explored as alternative to synthetic pesticides is urgently needed. Thus, the phytochemical screening, as well as the bioactivity of different polarity of organic solvents of leaf and stembark extracts of Trichilia heudelotii (Meliaceae), was investigated against the field-to-store insect pest Callosobruchus maculatus in laboratory bioassay. The non-polar (hexane) and polar (ethanol) extracts [0.0 (control), 0.5, 1.0 and 1.5 ml] of the leaf and stem bark were added to 100 g of cowpea. The following parameters of the cowpea weevil life cycle were analysed at the various concentrations: adult mortality, oviposition rate, number of larvae and pupae, and emergence of first filial progeny. The phytochemical screening revealed the presence of flavonoids, terpenoids, alkaloids, saponins in both the non-polar and polar extracts. Furthermore, the various treatments used were significantly (p< 0.05) effective in controlling C. maculatus from 1 and also 30 days after treatment (DAT) for both the non-polar and polar extracts when compared to the control. However, the most effective treatment was observed with the polar (EtOH) stem bark extract at 1.5 ml, which caused more mortalities and fewer emergence of the insect. Our findings suggest that the non-polar and polar leaf and stem bark of T. heudelotii extracts could serve as a sustainable and potential alternative to synthetic chemicals in pest control.