Insecticides for rice storage pests

While the `rice growers invest substantial amount of management practices (i.e., from land preparation to harvesting), one important factor that limit the quality of produce and ultimately profits is the damage of insect pests on stored grains. Estoy et al. (PhilRice-Agusan del Norte) [Philippines] conducted a study to evaluate the effectiveness of commonly available insecticides against storage pests such as rice weevil (Sitophilus oryzae) and the lesser grain borer (Rhizopertha dominica) under laboratory conditions. Eight insecticides were tested against the two major storage pests following the manufacturer's recommended dosage. These were Carbaryl (Sevin WP 85), Chlorpyrifos (Lorsban), Chlorpyrifos methyl (Brodan), Cypermethrin (Cymbush 5 EC), Deltamethrin (Decis-R), Imidacloprid (Confidor), Periphos methyl (Actellic 25 EC), and Malathion. Findings showed that Malathion was found to be most effective and economical in eliminating rice weevil population. In the study, no rice weevil was able to survive after 1 hour exposure to Malathion at a concentration of 40 ml/16 L water. Periphon methyl was the most effective against the lesser grain borer. With a concentration of 50 ml/16 L water, only 1.33 % of the insect population survived after 1-hour exposure. No insect survived after 12 hours. For residual toxic effect, Chlorpyrifos killed 100% of the rice weevil after 6 hours exposure at different concentration (20ml/16 L water, 35 ml/16 L water, and 40 ml/16 L water). In the evaluation of the residual toxicity of insecticides, the treated grains were kept for a week at room temperature. Rice weevil adults were then added and mortality was assessed after 1 hour, 3 hours, 6 hours, 12 hours, and 24 hours. The researchers concluded that Malathion and Periphos methyl are good grain protectors since these could eliminate rice weevil and lesser grain borer in a short time. The researchers also recommended the proper identification of insects in seed warehouses prior to the use of insecticides since different insects have different reactions to insecticides. Furthermore, they recommended a follow-up study on the development of resistance to insecticides.