Insecticide Resistance in Diamondback Moth

High levels of resistance to the major categories of insecticides, ie, organophosphorus, carbamates, pyrethroids, and DDT, have been detected in the diamondback moth in Taiwan. Synergist studies have provided insufficient evidence to show significant involvement of known metabolic systems, such as microsomal oxidation, esterase hydrolysis, and glutathione conjugation in organophosphorus and carbamate resistance. Meanwhile, moderate levels of reduction of acetyl cholinesterase sensitivity to these compounds have been observed. This, however, could not account for all the resistance detected. In addition, the relationship between carbofuran and carbosulfan resistance is discussed. While pyrethroid resistance is closely associated with microsomal oxidation, indirect evidence indicates nerve insensitivity may also be a contributing factor. Synergist piperonyl butoxide may temporarily obliterate pyrethroid resistance. But this effect disappears quite quickly, probably because of the development of resistance to this specific compound by the insect. Diamondback moth larvae selected with fenvalerate or fenvalerate/piperonyl butoxide seem to be more susceptible to some organophosphorus insecticides including mevinphos, profenofos, and prothiophos. Recommendations are suggested regarding the use of synergists, pyrethroids, and organophosphorus insecticides.