Baseline Susceptibility of Diamondback Moth Plutella xylostella L (Lepidoptera:Plutellidae) to chlorantraniliprole 18.5 SC in Tamil Nadu

The baseline susceptibility of diamondback moth, Plutella xylostella L. to chlorantraniliprole 18.5 SC was studied in the Insecticide Resistance Laboratory, Department of Agricultural Entomology, Tamil Nadu Agricultural University, Coimbatore. The median LC 50of chlorantraniliprole against diamondback moth larvae for F 1 population was 20.06 ppm and LC95was 835.68 ppm; whereas, the LC 50of F 25population was 0.91 ppm and LC 95was 23.11 ppm. The susceptibility increased up to F22population of diamondback moth without exposure to insecticides. The susceptibility index (SI) after F 25generation over F 1 generation was 22.02 and 36.15 based on LC 50and LC 95, respectively. The rate of resistance decline (R) was -0.0505 and the number of generations required for a 10 fold decrease of LC 50was 20. Based on LC 95 of F 25 population, a tentative discriminating dose (DD) was fixed as 23.00 ppm. P. xylostella resistance in three major cauliflower and cabbage growing areas i.e., Coimbatore, Oddanchatram and Udaghamandalam was monitored. Insecticides tested v i z. , chlorantraniliprole 18.5 SC at 23 ppm, spinosad 2.5 SC at 12 ppm, emamectin benzoate 5 SG at 2 ppm and quinalphos 25 EC at 3 ppm recorded high resistance levels during fourth week of January, 2013 and third week of February, 2013. Among the insecticides tested, chlorantraniliprole18.5 SC recorded low level of resistance with Udaghamandalam (53.83 %), Coimbatore (58.83 %) and Oddanchatram (64.00 %) population, whereas it was high in the case of emamectin benzoate, spinosad and quinalphos in the three regions.