Thirty-eight insecticides were evaluated in the laboratory by screening tests as oral toxicants for control of Leptinotarsa decemlineata (Say), and 27 were selected for comparative oral toxicity tests with 4th-stage larvae. Chlorfenvinphos, carbofuran, propoxur, dialifor, Bay 77049 (O, O-diethyl O-(2-quinoxalinyl) phosphorothioate), chlorphoxim, CGA 12223 (O, O-diethyl O-[l-isopropyl-5-chloro-1,2,4-triazolyl (3)] phosphorothioate), phoxim, and FMC 33297 (3-phenoxybenzyl (±)-3-[2,2-dichlorovinyl]-2,2-dimethylcyclopropanecarboxylate) in that order were more toxic than azinphosmethyl and endosulfan standards. Methidathion and PP 484 (diethyl-2-ethylacetamido-6-melhylpyrimidin-4-yl phosphorothionate) were comparable in toxicity to the standards, whereas the remaining insecticides were from 3–30 times less toxic. Greenhouse tests with 4th-stage larvae indicated satisfactory control with several insecticides at rates as low as 0.14 kg/ha (2 oz AI/acre), This was confirmed in microplot tests where azinphosmethyl, carbofuran, chlorfenvinphos, endosulfan. and methidathion applied at 0.14 kg/ha controlled all stages of this species within 24 h. DDT-resistance in populations of this species from southern Alberta had caused a 23-fold decrease in larval susceptibility to this insecticide. However, 10 years after the use of DDT was discontinued, larval susceptibility had returned to those levels recorded in 1957.