Evaluation of Combined Effect of Ocimum gratissimum and Ageratum conyzoides Leaf Powder as a Sustainable Bioinsecticide against Cowpea Weevil

Abstract

This study was conceived to improve the preservation of cowpea grains by eliminating the destruction of cowpea grains by cowpea weevils (Callosohruchus maculates) and to eliminate the detrimental effect of synthetic pesticide on the environment. This study evaluated the proximate and phytochemical composition of Ocimum gratissimum and Ageratum conyzoides leaves and the bioinsecticidal potential of dried leaf powder of each plant leaf and their combinations on cowpea weevils. Graded (0.25, 0.5, 1.00, 2.00 and 3.00 mg) of single and combined leaf powders of O. gratissimum and A. conyzoides were applied to uninfested cowpea grains, followed by the introduction of healthy adult cowpea weevils in the test chamber. Untreated grains served as the control. Behavioural responses and mortality rates were monitored for over 72 h. Mortality increased proportionally with dosage (0.25 < 0.50 < 1.00< 2.00 < 3.00 mg). Across all concentrations, the combined leaf powder induced the highest mortality, followed by A. conyzoides and O. gratissimum, indicating synergistic efficacy of the combined leaf powder treatment. The application of the two leaf powders, both individually and in combination significantly (P< 0.05) increased the mortality of C. maculatus approaching 100% after 72 h of exposure. These findings demonstrated that the leaf powder of A. conyzoides and O. gratissimum, particularly when used in combination, hold strong potential as effective bio-control agent for the sustainable management and control of cowpea weevil.