Injury

Potato foliage is the favorite food of the Colorado potato beetle, Leptinotarsa decemlineata, (Figure 1) followed closely by eggplant (Figure 3) and tomato. Adults and larvae will also feed on pepper and various weeds including groundcherry, jimsonweed, horse nettle, petunia, henbane, thorn apple, thistle, and mullein. Both the adults and larvae eat leaves, flowers, terminal growth, stems, and even fruit. Plants are often defoliated so completely that they die or produce poor yields.

Description

The adult is a broad, convex, hard-shelled beetle about 3/8-inch long and 1/4-inch wide (Figure 2). It is bright yellow in color with 10 longitudinal black lines on its wing covers and black spots on the thorax. The larva, or “slug,” is soft-skinned, hump-backed, very fat, and brick-red in color with two rows of black dots on each side of its body (Figure 1).

Life History

Adult beetles overwinter in the soil and emerge in early spring and lay bright, orange-yellow eggs in small clusters on the undersides of the leaves of host plants (Figure 2). The eggs hatch into larvae which feed for about 3 weeks, passing through four larval stages, the last of which enters the soil to pupate. Adult beetles emerge from the soil in about 1 to 2 weeks to lay eggs for a second generation. The process then repeats itself with second generation adults appearing in late summer. These adults feed before entering the soil for hibernation. Occasionally, a partial third generation may appear if fall weather conditions are favorable.

Management of Colorado Potato Beetles

• Hand picking adults and larvae and crushing egg masses can be effective. Destroy beetles by crushing or placing them in a can of water with a few drops of dish detergent (note: beetles secrete a reddish-orange fluid that can stain skin, so it is best to wear protective gloves). Do not just knock beetles off the plant as adults and larvae will readily climb back up the host plant if not destroyed.
• Floating row covers or insect netting placed over young transplants help protect tomato and eggplant foliage from beetle damage.
• Because beetles can migrate to the host plant after emerging from the ground in early spring, it is helpful to rotate solanaceous crops as far as possible from the previous year’s planting to reduce beetle infestations.
• A heavy straw mulch around plants may inhibit movement of early emerging adults, reducing early feeding and egg laying.
• For information on insecticides see FS1123, Vegetable Insect Control Recommendations for Home Gardens. Target newly hatched eggs and small larvae for best results. Thorough coverage of leaves and stems is important. Avoid overuse of insecticides as you may kill beneficial insects. Read and follow all pesticide label directions, restrictions, and pre-cautionary statements before using any pesticide. Remember that insecticides may be harmful to bees foraging in the area. Pesticide applications late in the day or at night will avoid actively foraging bees. Days to harvest after the last application vary depending on crop and pesticide. Refer to the label for appropriate time intervals.

This is based on the original work of:
Gerald M. Ghidiu, Ph.D., Extension Specialist Emeritus in Vegetable Entomology, Retired
Kristian Holmstrom, Vegetable IPM, Research Project Coordinator, Retired
Joseph Ingerson-Mahar, Vegetable IPM, Senior Program Coordinator, Retired.