Toxicity of Thiamethoxam and Imidacloprid as Seed Treatments to Parasitoids Associated to Control Bemisia tabaci

Abstract

Imidacloprid and thiamethoxam are being used for cotton seed treatment in cotton, Gossypium hirsutum L., to control various early season piercing and sucking pests. To assess the activity of these neonicotinoids against whitefly, Bemisia tabaci and their aphelinid parasitoids, cotton seed were treated with imidacloprid and thiamethoxam and sown in the field. Untreated seed were also sown as control treatment. The studies were continued for three years. During the study period, the population of B. tabaci remained below economic threshold level (6 leaf -1 ) in all the treatments upto 50 days after sowing. It was significantly lower in the imidacloprid and thiamethoxam seed treated plots compared with untreated check plots during the same period. Parasitism in the treated plots was comparatively lower than untreated plots. During 2003, the seasonal mean percent parasitism in plot treated with imidacloprid was 12% less than untreated plots. During 2004 and 2005, the level of parasitism in imidacloprid plots was 23.8% and 21.9% less and in thiamethoxam it was 15.9% and 18.4% less compared with untreated check. Total parasitism in pooled data from these studies revealed that percent parasitism reduction in imidacloprid (19.2 %) and thiamethoxam (13.2%) was less compared with untreated. Comparatively, thiamethoxam proved less toxic to parasitoids compared with imidacloprid.