Colorado Potato Beetle Leptinotarsa decemlineata (Say)

Kimberly Stoner
Department of Entomology
Connecticut Agricultural Experiment Station
123 Huntington Street
P.O. Box 1106
New Haven, CT 06504-1106

Telephone: (203) 974-8480 Fax: (203) 974-8502
E-mail: Kimberly.Stoner@ct.gov
Where and When to Look

Look for adults, larvae, and eggs on the leaves of potatoes, eggplant, and tomatoes. Adult beetles spend the winter under plant debris and in the soil. They emerge in late May, crawl to their host plants, climb up onto leaves, and begin feeding and laying eggs. Larvae begin hatching about a week later, and they also feed on leaves. A pupal stage of 5-10 days is spent in the soil. There are usually two generations per year in Connecticut.

Description

• Adult: Yellowish-brown round beetles about 1/2 inch long with ten black stripes on wing covers and black spots behind head.
• Eggs: Yellow or orange clumps of about 20 eggs laid on underside of potato or tomato leaves.
• Larva: Red to orange soft grub with black head, black legs, and, when large, two rows of black spots on each side of the body. Often found either on the underside of leaves or at the top of the potato plant.
• Damage: Adults and larvae feed vigorously on leaves. Potato plants can lose 15% of their leaf area without loss of yield, but an uncontrolled heavy population of Colorado potato beetles can kill all the potato plants in a field by mid-summer.

Control Methods

Natural: A bacterium that kills Colorado potato beetle larvae is available under many trade names, including Novodor, Foil, and Trident (Bacillus thuringiensis var. tenebrionis ). This bacterium is most effective when used on young larvae, so when you see adults, scout your fields for egg masses and newly hatched larvae, and apply the bacterium just when most of the eggs are hatching. Many insect natural enemies also feed on eggs or larvae and help to reduce the numbers of beetles.

In areas where potatoes are grown on a large scale, farmers are increasingly relying on physical methods to control beetle adults, especially as they walk into the field from the edges in the spring. One method is to dig ditches with steep sides lined with plastic mulch around the outside of a field. As long as the plastic is dry, there is a layer of dust on the plastic that keeps the beetles from being able to climb out of the ditch. Large numbers of beetles are trapped there, and die. Another method is to adapt propane flamers (used by some growers for weed control) to flame the beetles on young potato plants. If this is done at the proper speed with good equipment, the plants are minimally damaged, but the beetles and eggmasses are killed. The effectiveness of this can be increased by planting an early trap crop near a previous year’s potato field to attract early emerging adults and flaming the beetles on the trap crop, while the main crop emerges later elsewhere on the farm.

Various methods have been tried to make it more difficult for adult beetles to find and climb onto their host plants, including crop rotation, companion plantings of herbs such as tansy, and use of rough straw mulch. For rotation to be effective, the new field should be at least 200 yards from the old field. These tactics may delay the initial discovery of the plants by beetles in May. They do not provide complete control, so you should continue to scout the field to see if additional methods of control are needed. Straw mulch with well-timed application of Bacillus thuringiensis products may be a particularly effective combination.

Chemical: In addition to the bacterial insecticides, Sevin, rotenone, and pyrethrum are available in forms registered for control of Colorado Potato Beetle, but may not be effective due to the beetle's resistance to insecticides. A botanical insecticide based on neem, which has very low human toxicity (it is used in soaps and toothpaste in Germany), has been reported to be effective on Colorado potato beetle, and has recently been registered for food crops. Rotate insecticides with bacterial products to delay development of resistance. Follow instructions on the label.

Summary

The Colorado potato beetle is one of the most destructive insect pests of potatoes, and it can also be a pest of eggplants and tomatoes. Methods of control include the use of microbial insecticides derived from the bacterium Bacillus thuringiensis var. tenebrionis, physical methods such as propane flaming and ditches to collect dispersing adults, and cultural methods such as crop rotation and straw mulch. Many beetle populations have resistance to some widely used insecticides.

(revised 1/95)