Entomotoxicity of Oil Extract of Acacia auriculiformis (A. Cunn. Ex Benth) Used as Protectant against Infestation of Callosobruchus maculatus (F.) on Cowpea Seed

The insecticidal efficacy of Acacia auriculiformis oil extract in the laboratory at ambient temperature of 28±3 o C and 75±5% relative humidity. The oil of the plant was made by cold extract using ethanol as solvent. The oil was tested at 1, 2, 3, 4 and 5% concentration per 20 g of cowpea. The mortality of the insect was observed at 24, 48, 72 and 96 h post treatment. The oviposition and adult emergence of the insect as well as the seed damage, seed weight loss and weevil perforation index were observed. The result obtained showed that only 5% concentration of the oil achieved above 50% mortality of the insect at 96 h post treatment and its effect was significantly different from other concentrations and the controls. 4.91% of the oil was required to achieve 50% mortality of the insect within 96 h of application as reflected by the regression probit analysis. Likewise, the oil significantly reduced oviposition and adult emergence of the insect and as well reduced the seed damage, weight loss and WPI of the cowpea seeds. 5% concentration of the oil recorded lowest oviposition, adult emergence, seed damage, weight loss and WPI of 47.00, 24.08%, 17.77%, 10.45% and 20.93% respectively. There was great correlation between the adult mortality of the insect and the oviposition rate as well as between the adult emergence and seed weight loss as adult mortality and emergence determined 68.4% and 95.7% of the oviposition and adult emergence respectively. Since the oil of the plant has displayed high insecticidal potential, it could be incorporated into the integrated pest management technology.