Local variation in susceptibility of the diamondback moth, Plutella xylostella (Linnaeus) to insecticides and role of detoxification enzymes

The susceptibility of five different field populations of the diamondback moth collected as larvae within 15 km radius of Ottanchathiram and of the IARI 17-65 laboratory strain to Biobit(C) (Bacillus thuringiensis var. kurstaki HD-1), cartap, Cry1Ab, fenvalerate, fipronil, flufenoxuron and RH 2485 was studied using cabbage leaf disc feeding bioassays. All field populations were highly tolerant to fenvalerate and flufenoxuron compared with the IARI 17-65 strain. Monocrotophos tolerance in three field populations was about 3.7-4.5-fold higher than in the IARI 17-65 strain. All field populations showed 10-24-fold tolerance to cartap and 120-505-fold tolerance to fipronil compared with the IARI 17-65 strain. Wide variation in susceptibility of the field populations to insecticides appeared to be due to differential usage of these insecticides. Biobit((C)), Cry1Ab and RH 2485 were highly toxic to field populations of diamondback moth and could be used as alternate insecticides. An increased rate of detoxifying enzymes-hydrolases, transferases and oxygenases was responsible for imparting resistance in Plutella xylostella larvae to insecticides. These results emphasize a need for developing a location-specific insecticide resistance management. (C) 2003 Elsevier Science Ltd. All rights reserved.