Evaluation of the Efficacy of Ethanolic leaf extract of Vernonia amygdalina on the oviposition, egg hatchability and adult emergence of Callosobruchus maculatus(f.) on treated Cowpea seed

Abstract

The efficacy of Vernonia amygdalina ethanolic leaf extract against the oviposition, egg hatchability, and adult emergence of Callosobruchus maculatus (F.) on cowpea-treated seed was evaluated at the New Biology Laboratory, Department of Science Laboratory Technology, Kano State Polytechnic. Leaf extract from V. amygdalina was obtained by the Soxhlet extraction method. C. maculatus was obtained along with infested cowpea grains from Dawanau market in Kano State, Nigeria. The insects were reared in the laboratory, and four different concentrations of the leaf extract (1.0, 1.5, 2.0, and 2.5 g) were separately mixed with 20 g of cowpea in separate Petri dishes, corresponding to (5.0, 7.5, 10, and 12.5% w/w), respectively. A control treatment was also set up. Five (5) adult pairs of newly emerged C. maculatus were introduced into each Petri dish. Oviposition and egg hatchability of the female insect were significantly reduced on seeds treated with higher treatment levels (10.0 and 12.5% w/w) of the extract at (p < 0.05), in comparison with the control treatments. C. maculatus adult emergence from seeds with varying doses of V. amygdalina was significantly reduced (p < 0.05) compared to other treatments. V. amygdalina plant leaf extract recorded low oviposition (3.3 ± 0.10), low egg hatchability (0.33 ± 0.19), and lower F1 progeny adult emergence (0.00 ± 0.00) when compared with untreated control treatment (p < 0.05). Therefore, the plant has shown strong effectiveness similar to that of synthetic insecticides in preserving cowpea seeds against C. maculatus during storage. It was recommended that the government should encourage more planting of these plants that possess insecticidal properties.