Abstract:
The possible use of leaf powder of Olax zeylanica in managing the maize
weevil, Sitophilus zeamais was investigated in the present study. Mortality of
one week old adults was obtained for five different doses each for their
insecticidal effect (l.0, 2.0, 3.0, 5.0 and 7.5g) and fumigation toxic activity
(2.0, 3.0, 5.0, 7.5, 10.Og) separately. In each bioassay, the mortality was
recorded after 3, 6, 9, 12, 18, and 24 hours after they were exposed to
different doses of the plant powder. The results of both bioassays revealed
that the leaf powder of this plant elicited a very high insecticidal activity as
well as fumigation toxic activity in S. zeamais weevils. Mortality effect of the
powders on the weevils was found to be dose and time dependent. The
observations indicated that the adult mortality increased with the increase of
the exposure time and the dose. No mortality was observed 3 hours after the
exposure of weevils to leaf powder at all doses. A high mortality rate was
observed after 9 hours of exposure with all doses except for the lowest and
alOO% mortality was recorded with 7.5g after 24 hours. Fumigation toxicity
of plant powder against the weevils also gave similar results where no weevil
deaths were observed at all doses of leaf powder after 3 hours of exposure.
At the highest dose of 10.Og, 98% mortality was observed after 24 hours. The
overall results imply the strong possibility of using leaves of Olax zeylanica
as a potent bio-insecticide in protecting maize grains from S. zeamais
infestations.
