Evaluation of Imidacloprid and Acetamiprid against Toxoptera aurantii Boyer in Tea

Laboratory and field studies were carried out to evaluate the efficacy of imidacloprid and acetamiprid against aphids (Toxoptera aurantii Boyer) in tea. The bio-efficacy of both pesticides was evaluated in laboratory by Leaf-dip method. The 24 h, LC₅₀ and LC₅₀ values were 174.02 and 1788.78 ppm for imidacloprid and 84.62, 262.18 for acetamiprid, respectively. Field studies revealed that maximum reduction in population of aphids by imidacloprid and acetamiprid was achieved at the end of 14 and 7 days, respectively. Comparison of laboratory bioassays and field studies showed that imidacloprid has greater efficacy in field conditions as compared to laboratory bioassays. Acetamiprid showed greater efficacy in laboratory bioassays. Imidacloprid gave better control of aphid population than acetamiprid at lower dosage in field. Based on statistical analysis of field data, two sprays of imidacloprid (22.5 g a.i./ha) at 2 weeks interval is suggested for the control of aphid population in tea plantation.