A. Genetzky, E. C. Burkness and W. D. Hutchison
Department of Entomology, University of Minnesota

Introduction

photo of red turnip beetles

Hosts of the red turnip beetle, Entomoscelis americana, include: turnip, radish, rapeseed, mustard, canola and other cruciferous plants. Damage caused by this beetle can range from being restricted to small portions of the plant to entire defoliation or death. The adults are easily identified by their bright red color and their distinguishing black strips.

Identification

Red turnip beetle adults are generally 7 mm long with a bright red body. The head is covered with red and black spots, and there are three black strips that run longitudinally down its back.

Larvae hatch out of oblong, reddish-brown eggs. The mature larvae are 3/8 inch long with rough skin and a segmented body. The upper side of the body is usually a smoky black color while the underside is brown, and the entire body is covered with short hairs. Red turnip beetle pupae are bright orange in color.

Biology and Life cycle

The red turnip beetle over winters as an egg in the soil. During early August to late October, the eggs are laid singly or in groups in cracks in the soil near the plants. After two or three weeks, the eggs are fully matured but will not hatch until the following spring. Starting in March and continuing until early May, larvae will hatch and immediately begin to feed on the foliage of cruciferous plants-especially volunteer canola, rapeseed, mustard, or weeds (namely fix weed and wild mustard). They primarily feed in the daytime, and if disturbed will drop to the ground.

Fully developed larvae will return to the soil to form an earthen cell and pupate. They remain in the soil for approximately 14 days and emerge as adults. In late June, the adults will emerge and feed for about two or three weeks. After this feeding period, the adults will return to the soil for one month to rest only to reappear towards the end of July. Feeding damage done after this reemergence is usually not severe. Adults will continue to feed, mate, and lay eggs until late October. Each female is capable of producing 300 to 400 eggs a season and will lay them throughout the field. There is only one generation per year.

Damage

photo of red turnip beetle damage

Hosts of the red turnip beetle include: canola, mustard, rapeseed, turnip, radish, and other cruciferous plants. The amount of damage that occurs depends on the level of infestation by the red turnip beetle. It can range from light foliar damage where only portions of the plant are affected, to defoliation of entire plants, which are stunted or killed. The beetle feeds on the leaves, flowers, stems, and seedpods of plants. Damage is usually obvious starting from the edges of the field and slowly spreading throughout the field.

Management

Damage usually begins in fields that have heavy infestation of weeds or volunteer plants of the mustard family that were not treated with herbicide in the fall or spring. The beetle will start with volunteer plants and slowly move into adjacent fields; therefore, it is important to prevent this from happening by controlling cruciferous weeds and volunteer plants. If possible, do not underseed canola, rapeseed, or mustard with forages. The use of herbicides is also helpful to rid fields of weeds.

Cultivation also proves to be extremely useful in the control of this pest. A beneficial time to do this is during the fall to early spring. This will disrupt or destroy the eggs and the weeds, which are the food supply for developing larvae. In addition, cultivating during mid May to mid June can reduce larval populations.

The use of insecticides may be an option if the infestation occurs in newly seeded fields in June, but it is important to examine the field for the level of damage before deciding to spray. An insecticide can be restricted to the margins of the fields since this is where initial infestations occur.To ensure proper use of insecticides, also refer to the most recent edition of the Midwest Vegetable Production Guide (BU-7094-S).

Selected References