AbstractThe contact toxicities of 11 insecticides were determined with a Potter spray tower using adults of crucifer flea beetles (Coleoptera: Chrysomelidae) collected from three locations over a 3-year period. Flea beetles collected from an experimental farm at London, Ontario, where no insecticides had been used, were compared with those from canola-growing areas near Saskatoon, Saskatchewan, and Winnipeg, Manitoba. Lindane, in a seed dressing, is widely used in both Saskatchewan and Manitoba whereas carbofuran, as in-furrow granules, has been more heavily used in Manitoba than in Saskatchewan. The flea beetles from Winnipeg were significantly less susceptible to all three carbamates tested (carbofuran, carbaryl, oxamyl) than those from Saskatoon or London. Both the Winnipeg and Saskatoon flea beetles were significantly less susceptible to methamidophos than the London population but not to the other organophosphates, the organochlorine (endosulfan), or the pyrethroids that were tested. These differences may indicate resistance in the Manitoba population, but this low level would not affect the efficacy of the currently recommended insecticides. The results emphasize the need to develop control strategies that will minimize the chances that the level of resistance will increase.