Evaluation of the Potency of Azadirachta indica (Neem) Leaf and Fruit Powders as Natural Alternatives to Synthetic Insecticides in Controlling Callosobruchus maculatus (Fabricius)

Abstract

Background: The cowpea weevil (Callosobruchus maculatus) poses a serious threat as a significant post-harvest pest of stored cowpeas, causing quantitative and qualitative losses in sub-Saharan African countries. Control of these insects has relied on synthetic insecticides, which are costly, harmful to human health, and unsustainable due to the development of insecticide resistance. While there is increasing attention on using plant-based alternatives, few empirical studies have investigated the efficacy of Azadirachta indica (neem) fruit and leaf powder against this pest especially in the Upper East Region of Ghana. Aim: This study aimed to evaluate the insecticidal efficacy of neem fruit and leaf powder against C. maculatus. Methodology: Cowpea seed infested with adult weevils was treated with neem fruit and leaf powder (15 g, 25 g and 45 g each). Mortality rate and seed damage were determined at intervals of seven days for four weeks in a storage experiment. Results: The findings showed that both neem leaf and fruit powder caused significant (p < 0.05) increase in the mortality of cowpea weevils and significantly (p < 0.05) reduced the number of perforated seeds in the treated samples. Both the 25 g and 45 g treatments showed greater effectiveness than 15g.  The 45 g neem leaf powder had an average mortality of 8.0 ± 2.8, while the fruit powder attained a mean mortality of 14.50 ± 2.70. Conclusion: While a high concentration produced better results, there was no significant difference (p > 0.05) between the effectiveness of 25g and 45g. This shows that the optimum dosage required for effective control of cowpea weevils is 25g.