| dc.description.abstract | The experiment was conducted to study the effectiveness of leaf, bark and stem extracts
of eucalyptus as botanical insecticides for the control of rice weevil, Sitophilus oryzae L.
and lesser grain borer, Rhyzopertha dominica F. in the laboratory conditions during
March to October 2017. Methanol was used to prepare the extracts and four doses viz.
0.5, 1.0, 1.5 and 2.0% along with a control of the plant extracts were applied for insect
bioassay, residual and repellent effects. Results revealed that the stem extracts of
eucalyptus plant showed the highest toxic effect both for the rice weevil (mortality,
34.53%) and the lesser grain borer (mortality, 40.27%) whereas leaf extract showed the
lowest toxic effect for the rice weevil (mortality, 11.20%) and the lesser grain borer
(mortality, 17.43%). Mortality percentages were increased proportionally with the
increased time intervals. In case of residual effect for rice weevil, the highest number of
adult emergence was recorded in control (78.33) treatment. Stem extract showed the
lowest adult emergence (36.53) and the highest infestation inhibition on rice weevil
(67.42%). On the other hand, the highest number of adult emergence in control (100.0)
for lesser grain borer whereas the lowest (45.59) was in stem. Similarly, the highest
infestation inhibition was found 69.97% in stem also. Among the eucalyptus plant part
tested, stem extract showed the highest mean repellent effect for both rice weevil
(73.33%) and lesser grain borer (74.67%) whereas leaf extract showed the lowest mean
repellent effect for rice weevil (56.33%) and lesser grain borer (59.33%). On the basis of
repellency rate, it was found that stem and bark extracts were in the same repellency
class i.e. Class IV and leaf extract was in Class III. All the doses had direct toxicity,
residual and repellent effects but the highest response found at 2.0% concentration and
the toxicity was increased proportionally to the level of concentration. On the basis of
LD50 values, the stem extract showed the highest toxic effects against rice weevil and
lesser grain borer. Considering all the concentrations, the order of toxicity of different
parts of eucalyptus plant extracts against rice weevil and lesser grain borer were found as
stem> bark> leaf. | en_US |
