University of Illinois Extension

University of Illinois Extension

Hort Answers

Insect Damage

Cucumber Beetles
Acalymma vittatum and Diabrotica undecimpunctata howardi

4 (1 = rare 5 = annual)
5 (1 = very little damage 5 = plants killed)
Cucumber, squash, watermelon, and other vine crops.

Plants Affected

Cucumber beetle adults are yellowish and about1/4-inch long.The striped (Acalymma vittatum) and spotted (Diabrotica undecimpunctata howardi) cucumber beetles have black stripes or spots, as their names suggest. The striped cucumber beetle has very distinct stripes and a black underside; the western corn rootworm has a similar appearance but has blurry stripes and a yellow underside. The spotted cucumber beetle somewhat resembles the bean leaf beetle, but the two spots just behind the head on the spotted cucumber beetle are distinctly separate; although the pattern of markings varies on bean leaf beetles, the mark just behind the head is always a single, distinct V-shaped or triangular spot. Larvae of both cucumber beetle species feed on the roots of various plantsbut do not causeserious damage.

Adult cucumber beetlesare chewing insects that eat holes in leavesand cause window-paning ofleaves of cucumber, squash, watermelon, and other vine crops. Window-paning is caused when the beetle eats the lower surface and inside of the leaf, leaving the upper surface intact but causing it to turn brown. These insects (unlike the western cornrootworm and bean leaf beetle) transmit the pathogen that causes bacterial wilt of cucumber and muskmelon. Infected plants may wilt and die in midseason.

Life Cycle
Adult cucumber beetles overwinter wherever standing vegetation provides cover and protection. They move to newly emerging seedlings or transplants of cucumbers, squash, melons, and pumpkins in April to June, depending on latitude. Overwintered adults feed for a few weeks, and females deposit eggs in the soil at the base of plants. Larvae feed on roots for a few weeks, pupate, and emerge as adults in mid to late summer. In southern Illinois and similar latitudes, a second generation of striped cucumber beetles develops each season; only one generation occurs farther north. In much of Illinois only one generation of spotted cucuber beetles develops each season, and cold winters in the north may greatly reduce survival.

In home gardens, controlling cucumber beetles is often necessary to prevent transmission of bacterial wilt and early death of cucumbers and muskmelons. Infestations greater than 1 beetle per plant are often enough to transmit bacterial wilt to a large portionof plants in a garden, so control efforts should strive to keep populations low if disease prevention is the goal. Using floating row covers to exclude beetles from plants can provide protection until plants begin to bloom. At this time, row covers must be removed to allow bees to pollinate the flowers. Protecting the cucumbers and muskmelons in their early growth stages delays disease transmission and may allow at least a few weeks of harvest even if beetles reach the plants and transmit the pathogen later. Insecticides are labeled to control cucumber beetles in home gardens, and effective prooducts include Sevin (carbaryl), permethrin, Entrust (spinosad), and natural pyretrhins. Zucchini and Blue Hubbard squash are especially attractive to cucumber beetles and may offer some value as trap crops.

Related Resources
Home, Yard & Garden Pest Guide
U of IL - Distance Diagnosis through Digital Imaging
U of IL - Plant Clinic