The powdered samples were prepared by pulverizing the dried leaves and seed with the help of a grinder. The ground samples were passed through a 25-mesh sieve to obtain fine and uniform dust. The extracts were preserved in airtight jar and stored in a refrigerator until their use for insect bioassay.
Experiment: Effect of the plant powders on mortality of rice weevil on rice grain.
For this experiment, the grains were sterilized in an incubator, about 24 hour at 60oC to disinfect them. About 20 g of the fresh and un-infested rice grain was measured in electronic balance and transferred into translucent plastic bottle of 8×8 cm size. Thereafter 5 g doses of each plant power were thoroughly mixed with 20 g of rice grain in each plastic bottle. Freshly emerged adult were starved for 4 hour and 20 pairs of adult weevil were released in the treated grain plastic bottle .The plastic bottles were covered with piece of cloth sized of plastic bottle with rubber band. For control no extract was applied on grains. Mortality was recorded at 7 days interval in one month. Three replications were maintained in each treatment. The experiment was conducted at 270C and 73% relative humidity under laboratory condition.
Mortality, progeny and damage assessment assays To estimate mortality, the number of dead insects in each vial was counted at 7,14,21,28 and 35 days after
treatment. Rice weevil mortality was assessed as
Number of dead insect/Total number of insects x 100
Data on percentage adult weevil were corrected using
Abbott's [1925] formula