Insecticidal and residual effects of plant extracts on F1 progeny and potentiality as grain protectant of rice weevil, Sitophilous oryzae L.

Rice weevil (Sitophilus oryzae L.) is one of the major pests of stored commodities. The adult weevils feed on rice and the females lay eggs inside rice kernels. In the present study, n-Hexane, dichloromethane (DCM) and methanol extracts from karanja, Pongamia pinnata (L.); mahogany, Swietenia mahogani Jacq.; neem, Azadirachta indica and urmoi, Sapium indicum Willd.  were tested for their insecticidal and residual effects against this pest under laboratory conditions. Response varied with plant species. Firstly for the activity of toxicitiy, urmoi fruit extract showed the highest toxic effect (mortality, 51.53%) and mahogany leaf extract was lowest toxic effect (mortality, 25.78%) at 72 hours after treatment (HAT). Secondly for the residual activity, grains treated with urmoi extracts showed the lowest number of adult emergence (4.86), grain infestation rate (1.53%) and inhibition rate (53.48%) at 5 days after treatment (DAT). Between neem seed and urmoi fruit extracts, the lowest number of F₁ adult emerged (17.33), the least grain infestation rate (4.38%), and the highest inhibition rate (40.65%) was found in urmoi extract on rice grains at 20 days after treatment. These results increased with increasing time from 5 to 20 days after treatment (DAT). On the other hand, inhibition rate decreased with increasing of time. Results indicated that urmoi extracts were more effective than other plant extracts against adult insects. Urmoi plant extracts can be used for the protection of stored rice from infestations of rice weevil.

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