Cucumber Beetles

About Cucumber Beetles

Cucumber beetles are one of the most serious insect pests of cucurbit vegetables (e.g., cucumbers, melons, pumpkins, squash). Beetles feed on the foliage, flowers and fruit of host plants. Adult cucumber beetles may also transmit bacterial wilt, which causes plants to wilt and die.

Cucumber Beetle Description

Two species of cucumber beetles are common in West Virginia; the striped cucumber beetle, Acalymma vittatum, and the spotted cucumber beetle, Diabrotica undecimpunctata howardi. The striped cucumber beetle has a black head and yellow body with three black stripes on its back that extend to the tip of the abdomen. The spotted cucumber beetle is similar in appearance but has 12 black spots on its back. Both species are approximately 6 mm in size.

Cucumber Beetle Damage

Damage from cucumber beetles begins in spring with feeding by adults on the stems, cotyledons and emerging leaves of young cucurbit plants. During this time female beetles begin laying groups of oval, orange-yellow eggs in the soil near the base of plants. Once the eggs hatch, the larvae immediately begin feeding on plant roots. The larvae pupate in the soil and emerge later in the summer as adults. The new generation of adults feed primarily on the foliage and flowers of plants. However, if populations are high, the beetles will also feed on stems and fruit.

Adults of both species can transmit the pathogen that causes bacterial wilt in cucurbits. Bacterial wilt is a serious disease of cucumber and muskmelon, and to a lesser extent, pumpkin, squash and watermelon. Because there is no cure for bacterial wilt, infected plants should be removed immediately before other beetles can feed on the plant and spread the bacterium.

Cucumber Beetle Control

Various methods may be used to manage cucumber beetles in vegetable gardens. Planting cucurbit crops later in the season (mid-June) when germinating conditions are more favorable and after initial peak feeding activity can help reduce damage. Row covers can also be used early in the season to protect establishing plants; however, row covers will need to be removed once blossoms appear to allow for pollination by bees. The use of reflective (i.e., silver metallic) mulches can help repel cucumber beetles from young plants, reducing damage and transmission of bacterial wilt.

Trap crops consisting of early planted cucurbits (planted approximately two weeks before the main crop) can be used to attract overwintering populations of cucumber beetles. Similarly, trap crops consisting of more attractive host plants, such as Blue Hubbard squash, other varieties of buttercup squash ( Cucurbita maxima) and zucchini ( C. pepo), planted along field borders can also be used to attract adult cucumber beetles. Traps crops can then be sprayed with an insecticide to reduce or eliminate the need for insecticide applications in the main the crop.

Chemical options for control of cucumber beetles include numerous compounds in the pyrethroid (e.g., beta-cyfluthrin, bifenthrin, cyfluthrin, esfenvalerate, fenpropathrin, lambda-cyhalothrin, permethrin, zeta-cypermethrin), neonicotinoid (e.g., acetamiprid, imidacloprid) and carbamate (e.g., carbaryl) class of insecticides. Insecticides available for use in organic crop production systems include pyrethrum and kaolin clay (note: kaolin clay only discourages feeding and does not kill beetles).

Figure 1. Adult spotted (left) and striped (right) cucumber beetle (Photo courtesy of Daniel Frank).

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