Tissue distribution and biochemical characterization of carboxylesterases associated with permethrin resistance in a near isogenic strain of Colorado potato beetle

Abstract

The tissue distribution of carboxylesterases associated with permethrin resistance in Colorado potato beetle (Leptinotarsa decemlineata (Say)) was investigated. Most of the trans-[14C]permethrin hydrolyzing activity (i.e., 77-86%) was found in hemolymph and soluble fractions. Hemolymph fraction from the permethrin resistant strain contained significantly higher trans-[14C]permethrin-hydrolyzing activity than the susceptible strain, indicating soluble carboxylesterases involved in permethrin resistance. Through electrophoresis and chromatofocusing procedures, the p/4,2-4.8 carboxylesterases from hemolymph were determined to be most closely associated with this aspect of permethrin resistance. These carboxylesterases from the permethrin resistant strain showed 1.7-6.0 times higher permethrin hydrolysis activities than those from the susceptible strain. Electrophoretic comparisons and kinetic studies implied that higher activity in the permethrin-resistant strain is primary due to the overproduction of the carboxylesterases rather than any qualitative change. The overall level of permethrin hydrolysis, however, was very low (i.e., 5.6 pmol/hr/larva) even in the resistant strain. Hemolymph carboxylesterases were inhibited by permethrin in a reversible manner, suggestive of high-affinity binding of permethrin to the carboxylesterases. Therefore, a sequestration of permethrin by hemolymph carboxylesterases (e.g., pl 4.2-4.8 carboxylesterases) through high-affinity binding was proposed to be a major contributing factor of permethrin resistance in the permethrin-resistant strain in addition to the low level of permethrin hydrolysis.