Development of an analytical method for analysis of flubendiamide, des-iodo flubendiamide and study of their residue persistence in tomato and soil.

Flubendiamide is a new insecticide that has been found to give excellent control of lepidopterous pests of tomato. This study has been undertaken to develop an improved method for analysis of flubendiamide and its metabolite des-iodo flubendiamide and determine residue retention in tomato and soil. The analytical method developed involved extraction of flubendiamide and its metabolite des-iodo flubendiamide with acetonitrile, liquid-liquid partitioning into hexane-ethyl acetate mixture (6:4, v v⁻¹) and cleanup with activated neutral alumina. Finally the residues were dissolved in gradient high pressure liquid chromatography (HPLC) grade acetonitrile for analysis by HPLC. The mobile phase, acetonitrile-water at 60:40 (v v⁻¹) proportion and the wavelength of 235 nm gave maximum peak resolution. Using the above method and HPLC parameters described, nearly 100 % recovery of both insecticides were obtained. There was no matrix interference and the limit of quantification (LOQ) of the method was 0.01 mg kg⁻¹. Initial residue deposits of flubendiamide on field-treated tomato from treatments @ 48 and 96 g active ingredient hectare⁻¹ were 0.83 and 1.68 mg kg⁻¹, respectively. The residues of flubendiamide dissipated at the half-life of 3.9 and 4.4 days from treatments @ 48 and 96 g a.i. ha⁻¹, respectively and persisted for 15 days from both the treatments. Des-iodo flubendiamide was not detected in tomato fruits at any time during the study period. Residues of flubendiamide and des-iodo flubendiamide in soil from treatment @ 48 and 96 g a.i. ha⁻¹ were below detectable level (BDL, < 0.01 mg kg⁻¹) after 20 days. Flubendiamide completely dissipated from tomato within 20 days when the 480 SC formulation was applied at doses recommended for protection against lepidopterous pests.

Persistence and dissipation of flubendiamide and des-iodo flubendiamide in cabbage (Brassica oleracea Linne) and soil.

Flubendiamide belongs to a novel class of insecticide which controls lepidopteran pest complex of cabbage such as diamondback moth, cabbage white butterfly, cluster caterpillar etc. Being a newly introduced insecticide no information is available on its residue persistence in cabbage. A study was undertaken to evaluate the residue persistence of flubendiamide in cabbage and soil following 2 applications of flubendiamide 480 SC at the recommended and double the recommended dose of 24 and 48 g a.i. ha(-1). Initial residue deposits of flubendiamide in cabbage were 0.33 and 0.49 mg kg(-1) respectively. The residues persisted for 10 days from the both the treatments and dissipated with the half-life of 3.9 and 4.45 days, respectively. Des-iodo flubendiamide, a metabolite of flubendiamide, was not detected in cabbage at any time during the study period. Soil sample collected from the treated field after 15 days was free from any residue of flubendiamide or its metabolite.