Adults: yellow, elongate, 1/4-inch beetles with black heads and three wide black stripes on wing covers. Larvae: slender, white grubs. Found in United States west to Colorado and New Mexico; in Canada, west to Saskatchewan.
Adults feed on squash family plants, beans, corn, peas, and blossoms of many garden plants. The beetles swarm on seedlings, feeding on leaves and young shoots, often killing plants; they also attack stems and flowers of older plants and eat holes in fruit. Feeding can transmit wilt and mosaic viruses. Larvae feed on roots of squash family plants only, killing or stunting plants.
Adults overwinter in dense grass or under leaves, emerging in early spring to early summer. They eat weed pollen for 2 weeks, then move to crop plants, laying eggs in soil at base of plants. Eggs hatch in 10 days; larvae burrow into soil, feed on roots for 2 to 6 weeks, pupate in mid- to late summer. Adults emerge in 2 weeks to feed on blossoms and maturing fruit. One to two generations per year.
Remove and destroy crop residues where adults overwinter; cover seedlings or plants with floating row cover, and hand-pollinate covered squash family plants; pile deep straw mulch around plants to discourage beetles from moving between plants; for uncovered plants, apply kaolin clay, especially to leaf undersides, and reapply after rain; handpick or vacuum beetles; apply parasitic nematodes to soil to control larvae; as a last resort, spray with pyrethrin when adults are seen feeding on pollen in flowers.