PATTERNS OF INSECTICIDE RESISTANCE TO AZINPHOSMETHYL, CARBOFURAN, AND PERMETHRIN IN THE COLORADO POTATO BEETLE (COLEOPTERA, CHRYSOMELIDAE)

Twenty-four field-collected and five laboratory strains of Colorado potato beetle, Leptinotarsa decemlineata (Say), populations were tested for resistance to azinphosmethyl (organophosphorus), carbofuran (carbamate), and permethrin (pyrethroid). Our objectives were to determine the distribution and severity of insecticide resistance in Michigan; to detect any relationships between location and resistance; to assess possible cross-resistance relationships; and to identify populations for future studies of resistance mechanisms and inheritance. Most populations were heterogeneous for resistance to at least one insecticide; they had shallow regression lines and high variability. Populations with high permethrin resistance tended to have low levels of resistance to azinphosmethyl and carbofuran and vice versa. Three main patterns of resistance were apparent in the field. In pattern 1, the resistance ratio was high for permethrin but low for the other two insecticides, probably because of microsomal oxidase activity specific for pyrethroids. In pattern 2, populations had high levels of resistance to azinphosmethyl and carbofuran and low resistance to permethrin as a result of several mechanisms, including a carbofuran insensitive cholinesterase. In pattern 3, beetles were resistant to all three insecticides and with cross-resistance to DDT, again as the result of several resistance mechanisms. The observed patterns and underlying resistance mechanisms indicate highly diverse resistance mechanisms even within a relatively narrow geographic area. This complicates resistance management for this insect.