Abstract

                                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 LC50 of chlorantraniliprole against diamondback moth larvae for F1 population was 20.06 ppm and LC95 was 835.68 ppm; whereas, the LC50 of F25 population was 0.91 ppm and LC95 was 23.11ppm. The susceptibility increased up to F22 population of diamondback moth without exposure to insecticides. The susceptibility index (SI) after F25 generation over F1 generation was 22.02 and 36.15 based on LC50 and LC95, respectively. The rate of resistance decline (R) was -0.0505 and the number of generations required for a 10 fold decrease of LC50 was 20. Based on LC95 of F25 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 viz., 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.

Key words : Chlorantraniliprole, Plutella xylostella, Resistance, Monitoring