Colorado Potato Beetle
Order Coleoptera: Family Chrysomelidae
Adult: Similar size (3/8 inch long) and shape as lady beetle, but with yellow and black stripes (Fig. 8.1).
Figure 8.1 - Colorado potato beetles (CPB) have black and yellow stripes and a shape similar to ladybugs.
Egg: Small, bright yellow to orange ovals laid in clusters of about 20-45 on the underside of leaves (Fig. 8.2).
Figure 8.2 - CPB eggs are bright yelloworange and laid in clusters on the underside of leaves
Larva: About ½ inch-long when mature. Small bulbous larvae that are reddish in color with two rows of black spots along the side of the body (Fig. 8.3).
Figure 8.3 - CPB larvae are bulbous in shape, reddish in color, and have black spots.
Pupa: Oval in shape and cream to orange in color (Fig. 8.4).
Figure 8.4 - CPB pupate in the soil after larval feeding.
Overwintering adults emerge from under plant debris and in the soil around May in northern Utah. Females lay clusters of eggs on the undersides of leaves of potato, tomato, pepper, eggplant, nightshade, and other solanaceous plants. Larvae feed for 10-30 days, and then pupate in the soil. There are two to three generations per season.
Colorado potato beetle (CPB) adults and larvae feed on foliage and can defoliate plants if not controlled. The last (4th) instar larva causes most of the feeding damage (Fig. 8.5). Potatoes in the vegetative stage can usually tolerate up to 30% defoliation, but when tubers start to bulk, plants can tolerate no more than about 10% defoliation. Thus, it is crucial to manage CPB soon after flowering as this is when tuber bulking begins. Other CPB hosts include eggplant, tomato, pepper, and other nightshade or solanaceous plants.
Figure 8.5 - CPB larvae feed on potato foliage resulting in defoliation.
Start monitoring fields at crop emergence for the presence of CPB. Larvae prefer to feed at the tops of plants making it simple to scout by checking these areas when walking through fields. Because small populations are easier to manage than large ones, the goal is to limit population growth and spread.
- Crop rotation and sanitation. Crop rotation delays and reduces infestations. If potatoes follow potatoes, overwintering CPB will immediately infest the new crop. Destroy any solanaceous plant residues that may provide alternate food sources.
Damsel bugs and big-eyed bugs feed on eggs and young larvae; predatory stink bugs will attack larvae. Two bioinsecticides are effective on young larvae: the bacterium, Bacillus thuringiensis var tenebrionis (Bt), and the fungus, Beauveria bassiana.
CPB has developed resistance to nearly every class of chemicals. Thus, it is critical to carefully rotate insecticide modes of action. In spring, wait until eggs have hatched for the first application. Border sprays may provide a more economical choice, especially early in the season before populations increase and spread throughout fields.
Several economic treatment thresholds have been developed. In general, 1 adult or larva per plant early in the season may warrant control. After flowering/tuber bulking, treat when there are an average of 1.5 large larvae or adults per plant.
Figure 8.1, Ward Upham, Kansas State University, Bugwood.org
Figure 8.2, David Cappaert, Michigan State University, Bugwood.org
Figure 8.4, Whitney Cranshaw, Colorado State University, Bugwood.org
Figure 8.5, Whitney Cranshaw, Colorado State University, Bugwood.org