Manitoba Agriculture, Food and Rural Initiatives

Flea Beetle I

• Flea Beetle II

Biology

Flea beetle eggs are tiny, (0.4 mm or 1/20 in.), elongated, and yellow. The larvae are a dirty-white colour with brown heads. When mature, the larvae are slender, up to 6 mm (1/4 in.) long, with 3 pairs of short legs on the thorax. The pupae are white and about 2.4 mm (1/8 in.) in length.

The adult beetles are small, blackish beetles with a metallic or bright blue lustre, measuring about 2-3 mm (1/8 in.) in length. Some species are striped; others plain.

Flea beetles overwinter as adults under leaf litter, along fence rows, and in shelterbelts and woodlots. They become active in mid-to late May, feeding on volunteer canola and mustard or on weeds. Later, the flea beetles move to seedling canola or other cruciferous crops.

After mating and egg laying in early June, the overwintered adults begin to die off. The young larvae feed on the roots of the developing canola for 3 or 4 weeks. They are present from about mid-June to late July.

After feeding, the larvae form earthen cells in which they pupate. The new adult flea beetles begin emerging in late July and early August. These adults feed on the green tissue of suitable host plants that are still present. Feeding may continue into mid-October. However, by mid-September, most adults have usually entered a dormant, overwintering stage. Only one generation of flea beetles is produced each year.

May	June	July	August	September
Overwintering adults become active and start feeding	Adult feeding continues, egg laying completed	Larval feeding on roots, pupation in soil	New adults emerge and begin feeding	Adult feeding continues, adults begin overwintering

Scouting Techniques

Flea beetles chew small holes in the cotyledons or leaves, giving a "shot-hole" appearance. Losses include stand thinning, smaller and weaker plants, and delayed plant development. All of these losses contribute to reduced yield, especially if the weather is hot and dry.

Canola seedlings can withstand significant leaf area removal in the cotyledon stage under good growing conditions without significant reduction in yield. However, with heavy and continuous attacks, seedlings may wilt and die. Heavy infestations may destroy the entire crop and re-seeding may be necessary. Once the crop reaches the 3- or 4-leaf stage, the plants are usually well established and can outgrow the feeding damage. Also, the number of adult flea beetles often begins to decline at that time.

Flea beetle abundance and related damage can be assessed in a variety of ways. One can count the number of infested plants per metre of crop row, collect all beetles down the centre row of a test area, or count the number of feeding holes on collected leaves. However, the simplest method is to sample a representative series of plants and rank each as to the % damage of the cotyledon leaf surface. If you rank, for example, 100 plants, you can total the % damage for all of the plants and divide by 100 to get an average % damage.

Economic Thresholds

The threshold is when, on average, 25% of the cotyledon surface is damaged.

Control Tips

Clearing cruciferous weeds from shelterbelts and headlands may help by removing alternative sources of food. Removing vegetative trash from fields and ditches may also reduce overwintering sites.

Early planting in stubble, at a high seeding rate, will minimize the damage caused by flea beetles. Planting into stubble may also reduce feeding damage because of the cooler micro-environment created when the stubble shades the surface soil. The cooler surface temperatures may slow down flea beetle activity, reducing damage.

Flea beetles can be controlled by using seed treatments, granular seed placed insecticides, foliar insecticides, or combinations of these treatments.

For further information, contact your GO representative.