Base Line Toxicity of Lufenuron 5.4 EC against Diamondback Moth, Plutella xylostella L. for Resistance Monitoring

Studies were conducted to assess the baseline toxicity of lufenuron 5.4 EC on Diamondback moth, Plutella xylostella collected from three different locations in Tamil Nadu where cabbage and cauliflower crops are grown extensively. Acute toxicity of lufenuron indicated that the LC₅₀values from F₁ to F₈ generations declined from 15.41 to 3.21 ppm and LC₉₅ declined from 458.11 to 33.62 ppm. The susceptibility index to lufenuron based on LC₅₀ was 4.80, while it was 13.63 based on LC₉₅. Rate of resistance decline (R) when selection pressure was stopped was -0.085. With regard to number of generations required for 10-fold decrease in LC₅₀, it was calculated as 11.76. Considering the F₈ P. xylostella population as the most susceptible, the tentative discriminating dose arrived at was 33.62 ppm for lufenuron. Resistance monitoring studies indicated that the per cent resistance of P. xylostella ranged from the lowest of 6.12 in Kotagiri to the highest of 24.49 in Ottanchathiram.