The Colorado potato beetle, Leptinotarsa decemlineata, is a native pest of the Rocky Mountain region. For many years the Colorado potato beetle was not considered an important insect. It fed on native weed host plants such as sandbur (nightshade.) When the early pioneers moved westward they brought the potato with them. Since the potato is its preferred host, the Colorado potato beetle gradually infested most areas in the country where the potato is grown.
Description of Life History
Adult Colorado potato beetles are about three-eighths-inch long, one-quarter-inch wide, and somewhat rounded in shape. The head and shoulders are brownish orange to yellow and covered with variously shaped black markings. Ten black lines run the length of the yellow wing covers.
Colorado potato beetle adult.These beetles spend the winter buried 3 to 6 inches deep in the soil. In the spring, they emerge from their cells and begin to lay eggs. The female produces 300 to 500 eggs over a period of about a month, then dies.
Active leaf damage.The elongate orange eggs are arranged in clusters of 10 or more, usually on the undersides of host plant leaves. Eggs hatch in about a week. Small, dark grubs emerge and develop rapidly into orange or red humpbacked, full-grown grubs or larvae.
Colorado potato beetle eggs on leafThe larvae have two rows of dark spots along the sides of their bodies. There are four larval grub stages, which take about 2 to 3 weeks for completion. At maturity, the grubs stop feeding, drop to the ground, and change to a resting stage (pupa) in the soil. Adults emerge in a week or two. These mate and lay eggs for the second brood. In Washington there are two generations per year.
Larval stage.
Hosts
Although chiefly a pest on potatoes and sometimes on tomatoes, these beetles can survive on cabbage, eggplant, and many weeds when potatoes are not available.Damage
The adult and larval stages feed on foliage; however, the larvae do most of the damage. Extensive feeding on the leaves and stem tips can prevent tuber development in potatoes, or fruit development on other host plants and, therefore, reduce yields.Control
When the first adults emerge in the spring, potato plants have not yet broken through the ground. When potato plants are not available, beetles use weeds such as nightshade and groundcherry as a food source. After potatoes become available, the beetles leave the weed hosts for the potato. Elimination of these weed hosts, particularly in home gardens, offers a measure of control.
Home gardeners may find physical destruction of the beetles a useful approach when numbers aren't too high. Rotation every other year may be very useful under circumstances when potatoes or other hosts aren't grown annually in close proximity.
Biological control may be accomplished using a beetle-specific strain of Bacillus thuringiensis registered on potatoes. While controlling listed beetles, it is harmless to bees and other beneficial insects.
For current chemical recommendations, refer to the Pacific Northwest Insect Control Handbook, your local WSU Cooperative Extension County agent, Master Gardener program assistant, or Entomology Specialist.
Many insecticides registered for control of this pest are hazardous to bees, so if drift to adjacent flowering crops is a risk, consider a less hazardous alternative.
