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Both the spotted cucumber beetle, Diabrotica undecimpunctata howardii Barber, and the striped cucumber beetle, Acalymma vittata (Fab.), are native insects ranging from Mexico to Canada, though they tend to be most abundant and destructive in their southern range. Striped and spotted cucumber beetle adults feed on foliage and stems of young cucurbit seedlings all season long, causing reduced stands. Adults also harbor the bacterial wilt organism (Pseudomonas lachrymans) in the winter and transmit it during the growing season. They also help spread cucumber mosaic. Larvae injure plants by feeding on the roots and tunneling through stems. Description: The adult spotted cucumber beetle is about 6mm (1/4 inch) long with a bright yellowish-green body. The head, legs and antennae are black, and 12 black spots appear on the wings. Adult striped cucumber beetles are about 5mm (../images/16 inch) long, black and yellow in color, and have three longitudinal black stripes on the wing covers. Both have beaded antennae about 2 mm (1/16 inch) long. The eggs of both cucumber beetles are oval, orange-yellow in color, and are found in clusters of 25-50 on undersides of host leaves. The larva is about 12 mm (1/2 inch) long with a yellow-white, somewhat wrinkled body and six long, brownish-colored legs. Striped cucumber beetle larvae are more flattened on the top of the abdomen. The pupa ranges from white to yellow in color and is about 6 mm (1/4 inch) long.
Life Cycle: Unmated adults overwinter in neighboring woodlands under leaves and trash. Adults leave their winter sites in late March and lay eggs from late April to early June. Before cucurbits become available to adults, they devour cotyledons and stems. Larvae feed in the soil on stems and roots, become full grown in two to four weeks, and pupate in the soil. First generation adults emerge from late June to early July. A complete life cycle requires from six to nine weeks. There are two and sometimes a partial third generation each year. Host Plants: Cucumbers, cantaloupes, winter squash, pumpkins, gourds, summer squash and watermelons are preferred by adult striped cucumber beetles. They also feed on beans, peas, corn and blossoms of several wild and cultivated plants. Larvae develop on these and related cucurbits. The spotted cucumber beetle has a wider host range and, in addition to cucurbits, may be found on beans, peas, potato, beet, tomato, eggplant and cabbage. The larva is the well-known southern corn rootworm which feeds on the roots of corn, peanuts, small grains and many wild grasses. Damage: Adults feed on young seedlings, causing poor stands and reduced yield. They chew leaves and tender shoots, often girdling stems. They feed on blossoms as well, and late in the season will gnaw holes in the fruit. They are known carriers of bacterial wilt and vectors of cucumber mosaic. Control: Several cultural measures discourage cucumber beetles. Early plowing-discing removes vegetation and discourages egg laying. Delayed planting (more favorable germinating conditions) and heavy seeding rates ensure a good stand. These pests are usually not as troublesome in sandy soils. Wire or cloth screen protectors shaped like cones or row covers will keep beetles off of home plantings until plants are well-established. A foliar insecticide applied at the cotyledon stage will retard cucumber beetle feeding and encourage plant establishment. Where insects are abundant, additional foliar applications may be needed to prevent beetles from spreading bacterial wilt and cucumber mosaic. Be sure to read and follow all label instructions, including intervals between spraying and harvest. Some seed catalogs carry resistant plants which are adequate for homeowner problems with cucumber beetles.
Adapted from K.A. Sorensen, North Carolina Cooperative Extension Service, 1999
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