Abstract:
Powdered leaves of thirty seven plant species were screened under
laboratory conditions with the temperature of 29±2° C and 84±2 %
relative humidity for their repellent properties against rice weevil,
Sitophilus oryzae (L). The screening was carried out with the view
of producing more eco-friendly agents suitable for post-harvest rice
protection and as sustainable alternatives to synthetic pesticides in
the control of S. oryzae.
Reared weevils were exposed to 15.0 g of leaf powders admixed
with rice grains in laboratory screening test using a modified cupbioassay.
The results revealed that twenty treatments caused
significant repellency of adult s.oryzae than the control. Out of
these, Ocimum gratissimum (Lamiaceae), Cinnamomum verum
(Lauraceae), Mentha viridis (Lamiaceae), Plectranthus amboinicus
(Lamiaceae) and Citrus reticulata (Rutaceae) showed the highest
repellent activity. M. viridis elicited the highest and the strongest
repellency (89.0%) in the weevils when compared with the other
three treatments. However, the weevils demonstrated considerably
Laboratory Evaluation of Some Sri Lankan Plants as Post
high rates of repellency to C. verum, 0. gratissimum, C. reticulata
and, P. amboinicus which were 76.0%, 74.0% ,68.0% and 64%
respectively.
When weevils were further tested against 5.0, 10.0 and 15.0 g of
leaf powders, all treatments showed significantly (p < 0.05) higher
repellency of S. oryzae than the control. M. viridis at 15.0g dose
elicited the highest and the strongest repellency (89.0%) in the
weevils when compared with the other treatments and
concentrations. The overall results indicated that repellency rate
increased proportionately with the increase of the dose of the
powder. A similar trend of repellency was also observed with time.
However, the effects of all plant powders on the insects were
highest within 6 hours post treatment.
The overall results of the research provide scientific corroboration
for the use of the four plant powders as effective grain protectants
against the rice weevil.
