Background Agriculture being one of the major practices in the world has contributed to environmental pollution, especially in developing countries where there were no equipment to recycle the agricultural wastes. Considering the high level of infestation of paddy by Sitotroga cerealella and the high level of pollution caused by agricultural wastes, this research investigated the chemical composition and toxicity of agro wastes (rice husk, maize cob, groundnut and cowpea pods) as eco-friendly protectants of paddy against Sitotroga cerealella. Parameters assessed include adult mortality, oviposition, adult emergence and egg hatchability. Gas chromatography and mass spectrophotometry were used to isolate and characterize the active compounds present in the most effective crude extract. Results The results of the study revealed that all agricultural wastes showed high mortality effect on S. cerealella. Cowpea pod powder was the most toxic to adult paddy moth that caused 33.33%, 36.67%, 46.67%, 50% and 60% mortality of S. cerealella at concentrations 0.1 g, 0.2 g, 0.3 g, 0.4 g and 0.5 g/20 g of paddy grains after 24 h of exposure, respectively. The Cowpea pod, groundnut pod and maize cob extracts caused 100% mortality of S. cerealella at concentration 0.5 ml/20 g of paddy grains after 96 h of exposure, respectively. The lethal concentrations LC50 and LC90 of cowpea pod after 24 h were 0.16 and 0.64 ml which were the lowest of all agro waste extract tested. GC–MS analysis revealed that 19 chemical compounds were present in cowpea pod extract, 9, 12-Octadecadienoic acid (a methyl ester) has the highest percentage total of 39.57% and 4-Pentenal, 2-methylene (0.12%) has the least percentage total. Conclusion All the observations revealed that cowpea pod was the most effective. The findings also suggested that the selected agricultural wastes have a promising insecticidal potential and can be used as alternatives to synthetic chemical insecticides for the control of stored product insects.

Background The cowpea bruchid, Callosobruchus maculatus is the major postharvest insect pest of cowpea seeds in storage. This had led to huge losses and quality deterioration of stored cowpea seeds that serve as poor man’s meat in lieu of expensive meat source in developing countries. This research was carried out to evaluate the bioefficacy of rice husk, maize cob, groundnut, and cowpea pods against C. maculatus in the laboratory. Adult insect mortality, eggs laid, adult emergence, damaged seeds, weight loss and beetle perforation index (BPI) were evaluated. Phytochemicals of the wastes were investigated. Results The result showed that the agricultural wastes contained alkaloids (1.56–2.77 mg/g), saponin (1.51–3.38 mg/g), phytate (7.00–17.76 mg/g), oxalate (0.32–1.13 mg/g). All agricultural wastes showed a high mortality effect on C. maculatus, and their effects increased as the exposure time and concentration/ dosage increased. Beetle mortality was highest in cowpea pod with 80% mortality for powder after 3 and 4 days when applied at 0.5 g/20 g cowpea seed. This showed that cowpea pod powder has the greatest insecticidal activity while the least was observed in maize cob powder (73.33%). Fewer adults emerged with maize cob having the least emergence when applied at 0.2–0.5 g dosage. Extracts of all agricultural wastes tested against C. maculatus were able to affect 70–100% mortality after 4 days of application at concentration 0.5 ml with cowpea pod extract causing 100% mortality of beetle after 4 days of application. The calculated lethal dose (LD50 and LD90) and concentrations (LC50 and LC90) of wastes powders and extracts cowpea pod was observed to have the lowest lethal dose while maize cob wastes were the highest across all period of exposure. Conclusion Base on the results obtained, cowpea pod waste was the most toxic in biocontrol of C. maculatus.