Residue Dynamics Of The Insecticide Imidacloprid In Relation To Mortality Caused To The Brown Planthopper Nilaparvata Lugens (Stal) (Hemiptera: Delphacidae)

Imidacloprid is a foliar and systemic insecticide used for controlling hemipteran insect pests such as planthoppers and aphids. The extensive use of imidacloprid to control rice planthoppers has increased the risk of resistance development for many other insect pests in the rice agroecosystem. We measured insecticide residue concentrations in leaves and stems of two varieties of rice plants after either a water or foliar application and evaluated the efficacy of imidacloprid residues in plants for control of the brown planthopper, Nilaparvata lugens (Stal) in rice. The concentration of imidacloprid residues varied with application method, plant part and developmental stage of rice. Residue concentration in plants receiving insecticide as a water application was significantly higher than in plants receiving insecticide as foliar sprays. Residues were higher in fully expanded leaves than in unexpanded new leaves and stems. Residues were higher at the booting stage than at the tillering stage. Correspondingly, corrected control efficacy of imidacloprid residues against N. lugens for water application and all applications at the booting stage (52 days after rice transplantation) was higher than for foliar applications and all applications at the tillering stage (36 days after rice transplantation). By improving application methods, it may be possible to improve the efficacy of imidacloprid against N. lugens under field conditions.