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The cowpea beetle, Callosobruchus maculatus (Fabricus) (Coleoptera: Chrysomelidae), is a major pest of stored cowpea militating against food security in developing nations. The comparative study of Xylopia aethiopica and Aframomum melegueta powder in respect to their phytochemical and insecticidal properties against C. maculatus was carried out using a Complete Randomized Design (CRD) with five treatments (0, 1.0, 1.5, 2.0 and 2.5g/20g cowpea seeds corresponding to 0.0, 0.05, 0.075, 0.1 and 0.13% v/w) replicated thrice under ambient laboratory condition (28±2°C temperature and 75±5% relative humidity). The phytochemical screening showed the presence of flavonoids, saponins, tannins, cardiac glycoside in both plants, while alkaloids was present in A. melegueta and absent in X. aethiopica. The mortality of C. maculatus increased gradually with exposure time and dosage of the plant powders. X. aethiopica caused 75.15% adult mortality and A. meleguta exerted 85% mortality at 120 hrs post infestation. Maximum oviposition deterrent activity was observed with X. aethiopica (54.26%) compared to A. melegueta (51.32%). Conclusively, both plants showed highly useful bioactivity against C. maculatus in suppressing oviposition and adult emergence and, therefore, can be used in formulating ecofriendly herbal insecticides.

Background Powders and extracts of Piper guineense seeds and leaves were assessed for insecticidal activities against Callosobruchus maculatus in the laboratory at temperature and relative humidity of 29.6 °C and 75.9%, respectively. Bioactive compounds in P. guineense leaves and seeds were also investigated. The powders were tested at rates 1.0, 2.0 and 4.0 g/20 g cowpea seeds while extracts were tested at 1.0, 2.0 and 3.0%. Results Results of contact toxicity assay of the seed powder caused 100% adult mortality at 96 h post-treatment period whereas leaf powder evoked 90% adult mortality within the same period at concentration of 1.0 g/20 g cowpea seeds. Low adult emergence was observed on cowpea seeds treated with 1 g of seed powder with percentage adult emergence of 10.0% and inhibition rate (IR) of 97.5%. Beetle Perforation Index (BPI) obtained from treated cowpea seeds was significantly different (P < 0.05) from BPI of untreated seeds. Extracts of P. guineense seed were more toxic than seed powder. Piper guineense seed extract caused 87.5% adult mortality of C. maculatus while leaf extract caused 70.0% adult mortality within 24 h of infestation at concentration of 1%. Progeny development of C. maculatus was completely inhibited in cowpea treated with 2% and 3% leaf and seed extracts of P. guineense. β-Pinene was the most abundant active compound in P. guineense seed (55.6%) and leaf (48.4%). β-Phellandrene occurred 38.2% in seeds while Ocimene had the least value of 0.2% in seed and 0.5% in leaf. Conclusion The study showed that P. guineense seed powder and extracts were more effective than leaf powder and extract. Utilization of plant products as alternative to synthetic insecticides in protecting cowpea seeds against C. maculatus should be encouraged for enhanced food safety and security. Piper guineense is used as spice and medicine and interestingly safe for human use.

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The efficacy of oil extracted from the leaves of Secamone afzelii was evaluated in the laboratory against Callosobruchus maculatus infesting stored cowpea. Leaf extracts from S. afzelii were obtained through the soxhlet extraction method using methanol and hexane as the solvent. Each of the extracts was tested by exposing five pairs of adult beetles to various levels of 0.5, 1.0, 1.5 and 2.0 ml corresponding to 2.5, 5.0, 7.5 and 10.0% v/w concentrations admixed with 20g cowpea in three replications respectively, in a Completely Randomized Design (CRD). Control treatment was set along. The results showed that oviposition and percentage egg hatched were significantly (P <0.05) suppressed on seeds treated with higher treatment level of extracts. Leaf extract with hexane at 2 ml (10.0% v/w)/20g cowpea seeds was most effective in suppressing oviposition and egg hatched. Therefore, S. afzelii exhibit promising degree of oviposition deterrent and ovicidal properties and, thus, have a great potential for use as a plant-based biopesticide as an alternative to synthetic insecticides for controlling C. maculatus infestation on stored cowpea grains.