Insecticide Resistance in Field Populations of Cotton Thrips (Thrips tabaci Lindeman) in Major Cotton Growing Regions of Tamil Nadu

Field populations of Thrips tabaci Lindeman collected from different cotton growing areas of Tamil Nadu (South India) were bioassayed for their susceptibility to thiamethoxam, imidacloprid and dimethoate. The population of Kumbakonam was highly susceptible as evident from the lowest LC₅₀ and LC₉₅ values; the values being 0.0571 and 1.1446 for thiamethoxam; 0.0390 and 0.6914 for imidacloprid and 94.1882 and 999.0683 ppm for dimethoate, respectively. T. tabaci was highly susceptible to imidacloprid and thiamethoxam when compared to dimethoate. The Resistance Factor at LC₉₅ varied from 1.36 to 2.28, 1.21 to 2.84 and 1.91 to 4.82 for thiamethoxam, imidacloprid and dimethoate, respectively for all the populations. In general, the populations of T. tabaci exhibited low level of resistance to these insecticides.