Cucumber beetles are very common pests in vegetable gardens and may also attack ripening stone fruit. The most abundant species in California is the western spotted cucumber beetle, Diabrotica undecimpunctata; however, the similar western striped cucumber beetle, Acalymma trivittata, may also cause damage.
Identification
Adult beetles are shiny with black heads, long antennae, and about 1/4 inch long. Adults may be striped or spotted, depending upon species.
The western spotted cucumber beetle is greenish yellow and has twelve black spots on its back; the western striped cucumber beetle is yellowish orange and has three black stripes. Cucumber beetles may sometimes be confused with predaceous lady beetles, but can be distinguished by the antennae. Lady beetle antennae are short and stubby; those of cucumber beetles are long and threadlike.
Larvae are whitish and slender with three pairs of short legs; the head and tip of the abdomen are darker.
Life Cycle
Beetles overwinter as adults in weedy areas and move into planted fields and gardens as soon as plants start to come up. They lay their yellow orange eggs at the base of plants or in soil cracks. Hatching larvae burrow into the ground seeking out roots, feed for 2 to 6 weeks, pupate, and emerge as adult beetles that attack the aboveground portions of the plant. There are several generations a year.
Damage
Adults feed on the leaves of many vegetables as well as on soft fruit. Shoots and blossoms may also be consumed. Cucumber beetles may also spread cucumber mosaic virus or wilts in cucurbits. Larvae of the spotted cucumber beetle feed on the roots of corn, small grains, beans, sweet pea, and several grasses but do not usually cause noticeable damage in gardens. The striped cucumber beetle larva feeds exclusively on cucurbit roots and can damage these crops when infestations are heavy.
Solutions
Management of cucumber beetles is difficult. Most older plants can support substantial numbers without serious damage. The best strategy for most vegetable gardens may be to place protective cloth over emerging plants and remove it when plants are old enough to tolerate damage. On stone-fruit trees, early harvest may be the only option. Various general predators are known to attack cucumber beetles.
