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ABSTRACT
Leaf Powders from two tropical plants were evaluated, each for their mortality effects against the Maize grain weevil, Sitophilus zeamais. The plants used for the experiment were Jatropha curcas andOcimum gratissimum which were obtained from a community in Edo state. The leaf powders of both plants were applied at the rate of 1.0g, 1.5g, 2.0g and 2.5g/25g of maize grains for 72 hours in the separate experiments. Also, a control experiment for each leaf powder was set up to aid monitoring. Each plot consisted of a rubber cup containing 25g of maize grains and ten (10) unsexed adult S. zeamais. Each treatment and control was replicated four times. Observations were noted after every 12-hours interval. Results from both experiments shows that adult mortality increased as concentration of powder increased. Adult mortality was also found to increase as exposure duration increased. Significant differences (p < 0.05) existed among the plant powders and the concentration. A 67.50% mortality rate was obtained within 72 hours when J. curcas was applied at 2.5g/25g of grains. O. gratissimum was able to effect a 32.50% mortality rate at the highest concentration of 2.5g/25g of grain after 72 hours of exposure which is only lesser than the rate the lowest dosage (1.0g/25g of grain) of J. curcas elicited. This reveals that J. curcas had the greatest potency in controlling S. zeamais when compared to O. gratissimum which was less effective. Generally, the increase in mortality in insects treated with the leaf powders of both plantsas observed throughout the experiment indicates that the effect is directly proportional to both the exposure time, concentration used and also the toxicity of the plant used. This implies that the effectiveness of both plants leaf powders in controlling S, zeamais can be further enhanced by increasing the treatment dosages and also the exposure duration.
