The purpose of this dissertation was to determine the biochemical mechanisms of azinphosmethyl, permethrin, and abamectin resistance in the Colorado potato beetle (Leptinotarsa decemlineata (Say)) in the hope that this information may be used to construct resistance management strategies. Chromogenic substrates, as well as the in vivo and in vitro metabolism of the three radiolabelled insecticides, were used to determine the metabolic and pharmocokinetic differences of the strains. Azinphosmethyl resistance was due to reduced penetration of azinphosmethyl, increased monooxygenase activity towards azinphosmethyl, and an altered acetylcholinesterase. Monooxygenase activity appears to be the most important mechanism in azinphosmethyl-resistance, but reduced penetration and altered acetylcholinesterase probably have significant roles in the high level of azinphosmethyl-resistance in CPB. Permethrin-resistance appears to be due to increased carboxylesterase activity and site-insensitivity. An increased level of carboxylesterase activity was apparent from a higher $V\sb{max}$ towards carboxylesterase substrates and increased hydrolytic metabolites of permethrin. This carboxylesterase is membrane-associated. An isogenic permethrin-resistant strain was determined to be cross-resistant to DDT, indicating site-insensitivity was another mechanism involved in permethrin-resistance. Abamectin-resistance in two strains was determined to be polygenic. Both strains exhibited high levels of synergism to PBO and moderate levels to DEF. Both strains had elevated levels of cytochrome P450 and oxidative abamectin metabolites in vivo and in vitro. This is the probable reason for the higher levels of excreted compound in the abamectin-resistant strains. Carboxylesterase activity was greatly increased in the abamectin-resistant strains. Carboxylesterases may hydrolyze or sequester abamectin in the resistant strains.