Base-line susceptibility for six-day-old larvae of the diamondback moth, Plutella xylostella, against Bacillus thuringiensis var kurstaki (Biobit®) was studied by a cabbage leaf disc dip bioassay technique. Diamondback moth from 13 locations in seven different states spread over a distance of about 3000 km longitudinally was used for these studies. Forty-eight-hour LC50 values varied from 1.0 to 10.97 mg AI litre−1. Further investigations on the development of resistance under laboratory conditions showed an increase in LC50 from 2.76 (for unselected F1 generation) to 5.28 mg AI litre−1 (for selected F9 generation), using a selection concentration of 6.4 mg AI litre−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 tactics.
© 2000 Society of Chemical Industry