Bio-Residual Effects of Certain Compounds on the Cowpea Beetle under Store Conditions.

The cowpea beetles cause severe damage to legume seeds in storage. One of the most common control methods is mixing seeds with synthetic or natural agents to reduce heavy losses. This study was conducted to assess the residual toxicity of the evaluated compounds over a three-month storage period and to investigate the enzymatic activities of certain chemical agents in comparison with the organophosphorus insecticide malathion 1% dust against Callosobruchus maculatus. The results show that the mortality percentages decreased with increasing periods of exposure. Additionally,C. maculatus was more sensitive to kaolin and malathion than the other tested compounds. Based on the DT50 values, the tested compounds could be ranked as follows: Talc powder > thiamethoxam > lemongrass > B. bassiana > M. anisopliae. The highest persistent compound after kaolin and malathion was thiamethoxam, and the highest degradable compound was M. anisopliae after hexaflumuron and indoxacarb. The seed damage (%) recorded in all seed treatments was lower than that of the control during storage. Lemongrass EO achieved the highest protection after 3 months of storage and tested insecticides (thiamethoxam, malathion, hexaflumuron and indoxacarb). None of the treatments, including the control, had a significant effect on the germination percentages of treated cowpeas, except for lemongrass essential oil (EO), which significantly reduced germination. According to the findings, lemongrass EO significantly increased carboxylesterase (CarEs) and acetylcholinesterase (AChE) activity compared to other treatments. Lemongrass oil shows promise as a seed protectant; however, its dosage must be carefully controlled, as high doses may negatively affect seed germination and enzyme activity.