Cucumber Beetles
Spotted cucumber beetle, Diabrotica undecimpunctata howardi Barber; Striped cucumber beetle, Acalymma vittata (Fabricius), Chrysomelidae, COLEOPTERA


DESCRIPTION

Adult - Cucumber beetles are oblong-oval in shape and have beaded antennae about 2 mm long. Six mm long, the spotted cucumber beetle has a bright yellowish-green body with black head, legs, and antennae. Wings are marked with 12 black spots. Five mm long, the striped cucumber beetle is pale yellow with a black head and 3 black stripes down its back.

Egg - The oval orange-yellow eggs are found in clusters of 25 to 50 on undersides of host leaves. Each egg is about 0.6 mm long and 0.4 mm wide.

Larva - Cucumber beetle larvae have a yellow-white, somewhat wrinkled body with 3 pairs of brownish legs near the head and a single pair of prolegs near the tip of the abdomen. When fully grown, spotted cucumber beetle larvae are 13 to 19 mm long; striped cucumber beetle larvae are only 10 mm long and have a more flattened abdomen.

Pupa - Pupae are white, tinged with yellow and 6 to 8 mm long. A pair of black spines is located at the tip of the abdomen.


BIOLOGY

Distribution - These native insects occur from Mexico to Canada. They are most abundant and destructive in their southern range, but usually are not troublesome in areas with sandy soils.

Host Plants - Cucumber, cantaloupes, winter squash, pumpkin, gourd, summer squash and watermelon are preferred by adult striped cucumber beetles. They also feed on bean, pea, corn, and the 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 bean, pea, 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 - Striped and spotted cucumber beetle adults feed on the foliage and stems of cucurbits all season long. They often girdle stems by gnawing on the tender shoots of seedlings. As plants develop, beetles also feed on blossoms and leave scars on the fruit. Adult cucumber beetles harbor bacterial wilt organism (Pseudomonas lachrymans) in winter and transmit it during the growing season. They also help spread squash mosaic virus. Larvae injure plants by feeding on roots and tunneling through stems.

Life History - Unmated adults overwinter in neighboring woodlands under leaves and trash or around the bases of plants that have not been killed by frost. Adults leave their winter sites in late March. Before cucurbits are available, the beetles subsist on the pollen and petals of many plants. As soon as cucumber, squash, or melon vines appear, beetles devour cotyledons and stems. Females of the overwintering generation lay eggs from late April through early June, each female depositing as many as 500 eggs. Depending on temperature, eggs incubate for 7 to 10 days before hatching. Larvae feed in the soil on stems and roots for 2 to 4 weeks before pupating. First generation adults emerge from late June to early July. Over the next 6 to 9 weeks, the life cycle is repeated, second generation adults being prevalent from September to November. These later adults assemble on clover and alfalfa upon which they feed until winter. They may come out to feed during warm periods in January and February. Two generations and sometimes a partial third are produced each year.


CONTROL

Several cultural measures discourage cucumber beetles. First, early plowing-discing removes vegetation and discourages egg-laying. Delayed planting (more favorable germinating conditions) and heavy seeding rates ensure a good stand. Wire or cloth screen protectors shaped like cones will keep beetles off home plantings until plants get established.

The use of resistant varieties is perhaps the most important control tactic. The following cucurbit varieties are resistant to spotted cucumber beetles as seedlings and also have resistant foliage later in the season: Blue Hubbard (squash); Ashley, Chipper, Gemini (cucumber). The North Carolina Agricultural Extension Service publication AG25, Control Vegetable Insects Using Cultural Methods, gives a more thorough and extensive listing of resistant varieties. Use of resistant varieties may not give complete control where infestations are heavy.

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 squash virus. For recommended insecticides and rates, consult the current North Carolina Agricultural Chemicals Manual.

Return to AG-295 Table of Contents