AbstractAdults of five species of flea beetles were found attacking rape crops (Brassica napusL. andBrassica campestrisL.) in the Canadian prairie provinces from 1971 to 1974.Phyllotreta cruciferae(Goeze) was the most abundant and serious pest, followed in order byPsylliodes punctulataMelsh. andPhyllotreta striolata(F.) (=vittata(F.)), whilePhyllotreta albionica(Lec.) andPhyllotreta robustaLec. were present only occasionally. The fourPhyllotretaspecies confined their feeding largely to cruciferous plants, butPsyl.punctulatahad a broader host range. All of the five species overwintered as adults, usually in leaf litter or turf beneath hedges, poplar groves, or fencerows, or sometimes in the soil in fields, and all became active with the arrival of warm sunny weather in the spring, withPsyl.punctulatausually being the first to appear. All appeared to have but one generation per year, with mating and egg laying occurring in the spring, the larvae inhabiting the soil and feeding on host-plant roots, and the new generation of adults emerging from pupae in the soil in late July and in August. The overwintered adults usually died in late June or early July, so there was a period in July when adult flea beetles were scarce. The most serious damage to rape crops by flea beetles was caused by overwintered adults attacking seedling crops in the spring; movement of these beetles into crops took the form of a creeping infestation moving from plant to plant into the field from nearby volunteer rape of cruciferous weed feeding grounds, or a more rapid and even infestation of a whole field with flight probably being the major method of movement. Flea beetles fed most actively when the weather was sunny, warm, and dry; cool damp weather reduced the intensity of attack and aided plant growth. Shade, such as exists in a healthy stand of rape beyond the pre-bloom stage, also inhibited attack. Occasionally, late-maturing rape crops were damaged in late summer by new generation adult flea beetles, particularlyP.cruciferae, feeding on the green epidermis of the stems, leaves, and pods.A field key for separating the five flea beetle species attacking rape crops in the Canadian prairie provinces is given.