Evaluation of Methanol, Ethanol and Acetone Extracts of Four Plant Species as Repellents against Callosobruchus maculatus (Fab.)

Abstract

Methanol, ethanol and acetone extracts of leaves of four plants were evaluated for repellent activity against adult Callosobruchus maculatus using a multi-choice bio-assay apparatus. The experimental plant species studied were Ocimum gratissimum (L.), Ocimum sanctum (L.), Mentha viridis (L.), and Hyptis suaveolens (L.) in the family Lamiaceae. The extracts were applied to the food source (mung beans, 25 g) at 1.0, 5.0 and 10.0 ml concentrations and repellant activity was recorded. Observations were made after three hours for each solvent-plant extract and Percentage Repellency (PR) was determined. Among four study plant species and three solvents tested, methanol extract of M. viridis (10.0 ml) showed the strongest and highest repellent effect on C. maculatus (81%). With all three solvent extracts, the percentage repellency of the C. maculatus increased significantly with the increase of concentration producing the highest at 10.0 ml. When methanol and acetone based extracts were tested against the cowpea beetles, the highest percentage repellent activity was obtained with M. viridis followed by O. gratissimum and H. suaveolens respectively. The lowest percentage repellency was observed with O. sanctum. In contrast, ethanol-based extracts of O. gratissimum facilitated the highest percentage repellency (78%) and M. viridis produced the lowest percentage repellency (55%). Significantly high PR observed in all extracts strongly indicates the presence of repellent properties in all four plants. Solvents methanol and acetone appeared to be more effective in extracting bio-active compound/s from M. viridis whereas ethanol as a solvent seemed to be more efficient with O. gratissimum.