Studies on the fate of imidacloprid-a neonicotinoid insecticide in a rice ecosystem

摘要

Imidacloprid [1 -(6-chloro-3-pyridinylmethyl) - N- nitro imidazolidine-2-ylideneamine], a neonicotinoid broad-spectrum systemic insecticide, was recently introduced in India. It has a novel mode of action acting as an agonist of the nicotinyl acetylcholine receptor. This chloronicotinyl compound is very effective in controlling sucking insect, soil insects, termites and some species of chewing insects as well as seed dressing, soil treatments and foliar treatments in different crops. It is very popular in rice cultivation to control brown plant hopper (BPH). In order to determine the fate of the imidacloprid molecule in rice ecosystem, a field study was conducted at Bidhan Chandra Krishi Viswavidyalaya Research Farm, for two consecutive seasons (2002 kharif and 2003 rabi). Imidacloprid was applied in a rice field at the normal dose-rate of 17.8 g a.i. /ha, and at 35.6 g a.i. /ha on three occasions at intervals of 10 d and an untreated control was included. Soil samples were taken at an interval of0, 5, 10 and 30 d, and rice water samples were drawn 0, 3, 7 and 10 d after the last application along with straw and grain at harvest. All the samples were extracted, cleaned and characterised by hplc coupled with UV/VIS detector. The study revealed that the dissipation of imidacloprid in soil followed 1st order kinetics and DT50 values ranged from 3.16-4.04 d. The estimated water phase dissipation half-life was found to be 1.91 d irrespective of treatment and season. No residue could be detected in rice straw and grain at harvest.