Susceptibility pattern and development of resistance in the diamondback moth, Plutella xylostella L, to Bacillus thuringiensis Berl var kurstaki in India

Base-Line susceptibility for six-day-old larvae of the diamondback moth, Pl utella xylostella, against Bacillus thuringiensis var kurstaki (Biobit(R)) was studied by a cabbage leaf disc dip bioassay technique. Diamondback moth from 13 locations in seven different states spread over a distance of abou t 3000 km longitudinally was used for these studies. Forty-eight-hour LC50 values varied from 1.0 to 10.97mg Al litre(-1) Further investigations on th e development of resistance under laboratory conditions showed an increase in LC50 from 2.76 (for unselected Fl generation) to 5.28mg AI litre(-1) (fo r selected Fg generation), using a selection concentration of 6.4mg Al litr e(-1). This suggested a possibility of the development of resistance under field conditions if there were to be extensive and indiscriminate use of B thuringiensis. These findings are discussed in relation to integrated pest management and the mechanisms of resistance in resistance management tactic s. (C) 2000 Society of Chemical Industry.