.

Ethanolic oil extracts of Ocimum gratissimum was evaluated for their contact and fumigant toxicity against the wheat grain weevil, Rhyzopertha dominica and damage to stored wheat under laboratory conditions. Bioassays were conducted at five dosages, 1% of plant extract at 0.2, 0.4, 0.6, 0.8, and 1.0 ml/20 g wheat grains. Adult mortality, adult emergence including inhibition rate and seed weight loss in percentages due to infestation by the weevil were parameters assessed. Results indicated that, both tests at 1.0ml achieved 98-100% weevil mortality at 24 h and not significantly (P< 0.005) different from other concentrations and the negative control, but significantly different from the positive control. It was evident from the results that Ocimum gratissimum had significant effect on the survival of the insects as low dosage is required to achieve 50 and 95% mortality in 24 h. Weevil mortality and percentage inhibition rate increases with increased plant oil dosages, while adult emergence and percentage seed weight loss reduced with increased plant oil dosage. Findings from this study shows that oil extract of O. gratissimum could serve as a biopesticide for the control of adult R. dominica infesting stored wheat grain. Keywords: Bioassays, emergence, mortality, Ocimum gratissimum, Rhyzopertha dominica toxicity.