Persistence and Efficacy of Cypermethrin against Tribolium castaneum (Herbst.) in/on Stored Rice (Oryza sativa L.)

Laboratory studies were undertaken to explore the possibility of using cypermethrin as grain protectant for rice (Oryza sativa L.) during storage from its persistence and efficacy point of view. Insecticide was sprayed @ 15 and 25 mg ai m⁻² on the surface of the jute bags filled with rice grains. Residues in/on rice grains were 0.092 and 0.112 mg kg⁻¹ after one month from 15 and 25 mg a.i. m⁻² treatments and reduced gradually by 52–53% from both the application rates after 6 months of storage. Residues of cypermethrin on jute bags surface were found quite high even after 6 months of treatment (4.27 and 6.92 mg m⁻² from 15 and 25 mg a.i. m⁻² treatments). However, the residues left on bags surface after 6 months might not be enough to protect rice grains if to be stored further. The mortality of Tribolium castaneum Herbst ranged from 91.7 to 98.3% upto a period of 3 months. Washing of 0 d treated samples with water dislodged 21.57 to 24.19% cypermethrin residues while washing followed by steaming/cooking of the rice brought almost double the reduction in residues.