THE ROLE OF METABOLIC ENZYMES IN INSECTICIDE-RESISTANT COLORADO POTATO BEETLES

Several metabolic enzymes were assayed in susceptible and insecticide- resistant (R-mfo and R-AchE) strains of the Colorado potato beetle (Le ptinotarsa decemlineata Say). We compared the activities of esterases, glutathione transferases and mixed function oxidases, and measured in -vivo metabolism of carbofuran to determine the contributions of metab olic factors to the observed resistance. There were no substantial dif ferences between strains in alpha- or beta-naphthylacetate hydrolysis, or in glutathione transferase activity. Compared to the susceptible s train, the R-mfo strain showed 4-fold higher activity in both ethoxyre sorufin-O-dealkylase, and pentoxyresorufin-O-dealkylase activity. The R-AChE strain had a 1-5-fold higher level of ethoxyresorufin-O-activit y. Correspondingly, the in-vivo metabolism of carbofuran was highest i n the R-mfo strain, and the R-AChE strain was slightly higher than the susceptible strain. These results are discussed in relation to other resistance mechanisms which we have examined in these strains.