Here's information from UW-Extension:

For Immediate Release

Colorado Potato Beetle Update

The Colorado potato adult beetles have been spotted in Eau Claire County once again. These beetles are also found on tomato and eggplants. They have a hard rounded shell that is bright yellow with black stripes running the length of their backs and black spots behind their heads.

Erin LaFaive, Eau Claire County Extension Horticulture Educator, says “Knowing the lifecycle of these beetles helps to increase the chances of effectively managing this pest. This is true for many garden pests. Usually by the time your crops are affected from a pest or disease it’s too late to reduce the problem. Prevention and early detection is key.”

The adults and larvae are leaf feeders usually starting on younger leaves and working their way up to older leaves. Potato plants can tolerate some defoliation before the yield becomes affected with flowering plants tolerating 5-10% defoliation and after flowering, plants can tolerate up to 30% defoliation.

Females lay small bright yellow-orange eggs in clusters of 15-25 on the underside of a leaf. The larvae will molt or shed four times before becoming a beetle. Each one of these four stages is called an instar. The first instar hatch 4-9 days after being laid on the leaf and begin feeding. At this stage the blackish-brown larvae are so small that their feeding is not damaging to the plant. During the second instar the brown-red larva are small and feeding is still minimal. The third and fourth instars are when treatment becomes necessary. The third instars are reddish-brown with black heads and legs and black spots along the sides of their bodies. This whole process takes 2-3 weeks after which they return to the soil to pupate. The beetles emerge in 10-14 days in mid-July as adult beetles.

Check for the beetles in May after potato plants have emerged and keep checking until the end of July. Look under the leaf for the yellow-orange eggs and if found simply brush them off. Hand picking the adult beetle can be effective, but be sure to wash your hands afterwards as the Colorado potato beetle has a chemical that can burn and blister sensitive skin. Row covers and plastic-lined trenches help to prevent adult beetles from finding plants and laying eggs. Get rid of weeds around the garden that are in the same family as potato and eggplant such as nightshade, groundcherry, jimsonweed, horsenettle, and mullein as the beetles will eat lay eggs on these too.

Phil Pellitteri, UW Entomologist, says, “Most of the older chemicals such as Sevin do not work. Only three products will help homeowners combat the problem, the new Ortho Max with acetamiprid; BT, san diego strain, will kill small larvae; and spinosad products work best on the young larvae but is not as effective on adults.” Fourth instar ( larger larvae) are much harder to kill. Please read pesticide labels carefully and follow the instructions.