Abstract
Field colonies of the diamondback moth (DBM) from various areas in Thailand have commonly developed moderate to low levels of resistance to anti-cholinesterase compounds, but the tolerance for other insecticides was unexpectedly low, and these were recognized as a sign of resistance. The increase in resistance of a field colony selected with chlorfluazuron resulted in high resistance in a comparatively short time. On the release from chlorfluazuron selection for six generations, the strain showed a rapid decrease in resistance. The growers have commonly used Bacillus thuringiensis (B.T.) products and abamectin which have peculiar mode of action compared to that of conventional insecticides with short time interval for control of DBM. Hence, low resistance levels of DBM to conventional insecticides is due, at lease in part, to the replacement of these insecticides with B.T. and abamectin, and to the fact that field colonies have recovered sensitivity under cessation of these conventional insecticide pressures.
