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.
