Monitoring of insecticide resistance in diamondback moth based on cholinesterase genotype

Possibility of monitoring insecticide resistance in the diamondback moth by analyzing the insensitivity of cholinesterase (ChE) which is resistant to organophosphates and carbamates was investigated. Four kinds of ChE genotypes were found and inherited by incomplete dominance factors. Against propoxur and monocrotophos, each ChE genotype showed LD50 in proportion to the values of I50. Difference of I50 values in four kinds of ChE genotype to various ChE inhibitors was highest for methomyl(30 times), and very low for carbofuran and metolcarb(2–3 times). There is no sensitive ChE to both insecticides or very few in this strain. We also investigated other insecticide resistant strains and populations collected in the fields. IGR resistant and susceptible strains collected in Thailand and representative Japanese susceptible strain possessed only sensitive ChE. In two diamondback moth populations collected in Japan in 1992 and 1993, there were very few sensitive ChE, but more insensitive ChE. Existence of various types of ChE in the diamondback moth collected in fields means a potential to develop insecticide resistance by insecticide selection. As insecticide sensitivity changes from a low to 30 times according to ChE genotypes, it was considered that ratios of ChE genotypes were quickly affected by insecticide selections.