Entomoscelis americana Brown Coleoptera Chrysomelidae

Natural History

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.

  1. The eggs are deposited in August and September. They are elliptical, measuring about 1.5 mm long, and are red or brown. Eggs are deposited on the soil surface, or in the soil to a depth of about 12 cm. The eggs may be laid singly or in small clusters. They hatch in the spring, usually in March or April. The lower temperature threshold for development is about 5°C, and the upper limit about 37.5°C (Gerber and Lamb, 1982), but they hatch successfully over a broad range of temperatures (Lamb et al., 1984). The eggs tolerate cold temperatures very well; soil temperatures as low as — 10°C have no effect on survival (Gerber, 1981).
  2. The larvae are wrinkled in appearance, and initially are orange with black spots, but as they mature they become black. They initially are 1-2 mm long, but eventually attain a length of about 12 mm. There are four instars, requiring 6.9, 5.1, 5.0, and 14.9 days, respectively, for their development. Larval development, which often requires about 30 days, is usually complete by late May. Larvae feed principally at night.
  3. Pupation occurs in the soil at a depth of 23 cm. The pupa is orange, and 6-10 mm long. Duration of the pupal stage is about 15 days.
  4. The adult is distinctively marked with black and red. The ventral surfaces are primarily black, but the dorsal surface is red marked with black. The dorsum is marked with a small-black spot at the back of the head, which is contiguous with a large black spot in the center of the pronotum. The prono-tum also bears a small black spot on each side of the pronotum. There also is a black stripe running about two-thirds the length of each elytron. A narrow black stripe runs along most of the center of the back, where the elytra join dorsally. Thus, the overall appearance is a red beetle with a black spot near the head and three black stripes on the elytra. Beetles measure about 10 mm long. Adults appear intermittently, first in June and July, and then again in August until late October or the onset of cold weather, when they perish. Adults are reported to invade crops by walking rather than flying.
Adult red turnip beetle.

The biology of red turnip beetle was given by Chittenden (1902), Gerber and Lamb (1982), Gerber (1981,1989), and Gerber and Obadofin (1981a,b).

Damage

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).

Management

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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