Distribution. Red turnip beetle occurs in the United States from Minnesota and Wisconsin west to Colorado and Washington. In Canada, it is known from the Prairie Provinces, British Colombia, and northward. It is considered to be native to western North America, and limited in its distribution by a combination of weather and host plant availability (Gerber, 1989).
Host Plants. This is a crucifer-feeding insect. Vegetable crops attacked include broccoli, Brussels sprouts, cauliflower, cabbage, kale, kohlrabi, mustard, radish, turnip, and watercress. It also feeds on rape (canola) and horseradish. As rape has assumed greater importance as an oil-seed crop, red turnip beetle has increasingly become a more abundant, and serious, pest in Canada. Cruciferous weeds are suitable hosts, and feeding has been reported on shepherdspurse, Capsella bursa-pastoris; pepperweed, Lepidium spp.; wallflower, Erysimum parviflorum; and the mustards Erucastrum, Sisymbrium, and Brassica spp. However, Gerber and Obadofin (1981a) determined that black mustard, Brassica nigra; flixweed, Descurainia sophia; and tall hedge mustard, Sisymbrium loeselii; were marginally suitable.
Natural Enemies. No parasites are known, and the incidence of predation by carabid beetles and microsporidan disease is slight (Gerber, 1989).
Life Cycle and Description. Red turnip beetle has an unusual life history because the adult period is interrupted by a summer aestivation. There is one gen eration per year, and the egg is the overwintering stage. Larval and pupal development occur in the spring, with adults emerging in June. The adults do not oviposit immediately, however, but feed for a month and then enter a period of aestivation in the soil. They re-emerge later in the summer, mate, and oviposit.
The biology of red turnip beetle was given by Chittenden (1902), Gerber and Lamb (1982), Gerber (1981,1989), and Gerber and Obadofin (1981a,b).
The larvae cause damage by feeding on the cotyledons, leaves, petioles, and stems of seedlings early in the growing season. Later, both larvae and adults feed on foliage, eating large, irregular holes in the leaves. This is principally a pest of homegardens rather than commercial vegetable crops. It commonly is of concern to oil-seed producers, but the impact is often slight (Gerber, 1976).
Cruciferous weeds and volunteer crucifer crops can be important sources of insects in the spring, so clean cultivation is advisable if this insect previously has been abundant. Although this can be effective by denying larvae a source of food, if adults are present the destruction of weeds and volunteer cruciferous crops may drive the beetles onto the primary crop. Tillage may also destroy some of the overwintering eggs. If adults or larvae are abundant in the spring, foliar application of insecticides is an effective remedy. Row covers will also prevent invasion of vegetable gardens.
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