Phytochemical analysis and pesticidal effects of Ocimum gratissimum leaf oil extract in the management of Callosobruchus maculatus infesting Vigna unguiculata.

Abstract

The study aimed at evaluating the phytochemicals present in the leaves of Ocimum gratissimum, V. amygdalina, P. guineense, G. latifolium and A. indica harvested from farms at Anaku in Ayamelum LGA of Anambra State and subsequently test their potency in causing mortality and reducing loss and damage due to C. maculatus infestation. Phytochemical analysis of the plant materials, leaf oil extraction and pesticidal studies were carried out in the Laboratory. Five serially diluted concentrations (1.25 % v/v, 2.5 % v/v, 5.0 % v/v, 10 % v/v and 20 % v/v) of the leaves oils extracted with N-Hexane were used. The experiment also has two control treatments (CI – acetone only and C2 – no treatment). The data collected on insect mortality, seed damage and weight loss were analyzed using Analysis of Variance (ANOVA) separated using the Student–Newman-Keuls (SNK) test. The highest corrected mortality, 100.0% was recorded at concentrations ≥ 5.0 % v/v. The least corrected mortality, 66.7% was recorded at 1.25% v/v concentration. Bean seeds treated with a 20.0% concentration of the oil extract recorded the least percentage of damaged seed and weight loss with a Mean±SE value of 8.3±0.8 while Bean seeds treated with a 1.25% concentration of the oil extract recorded the highest percentage of damaged seeds and weight loss with Mean±SE value of 22.2±1.9. The five plants showed a similar level of performance in the management of C. maculatus with O. gratissimum having the best overall performance. Their pesticidal activity is related to their phytochemical constituents and their bitterness.