Southern Corn Rootworm
Egg - The egg is dull yellow, oval and about the size of a pinhead (0.6 mm).
Larva - The mature larva is 15 to 16 mm long with a yellowish-white, somewhat wrinkled body. It has six tiny, brownish legs and a brown plate on top of its last abdominal segment.
Pupa - About 6 mm long, the pupa is white to yellow.
Host Plants - Southern corn rootworms have been found on more than 200 plants including common weeds, grasses, and cultivated crops. This insect is prevalent on corn and peanut, but it also attacks cucumber, squash, bean and other vegetables, melon, wheat, rice, millet, rye, oat, and alfalfa.
Damage - The southern corn rootworm is the most serious insect attacking the roots and pods of peanuts in the southeastern Coastal Plain. This pest is most injurious to peanuts grown in heavy, poorly drained soil. It is frequently destructive to peanuts following a winter cover crop, such as vetch or crimson clover. More damage occurs in fields where peanut foliage is heavy than in those where foliage is light.
The larvae bore into the pods of the peanuts and feed on the kernels. They prefer young pods but will often attack the tips of the shoots or pegs and kill them before the pods develop. Occasionally, when pods are scarce, they attack stems. Fungi and bacteria may enter injured pods and cause decay.
Adults, known as spotted cucumber beetles, feed on the unopened leaves. After the damaged leaflets open, oblong to slightly irregular holes appear. Although not as injurious as the larvae, the beetles are sometimes minor pests.
Life History - The adults overwinter in and around the bases of plants or other protected places. Adults become active about the middle of March, and their eggs are laid from late April to early June. The eggs are laid singly, each female laying as many as 500. They hatch in 7 to 10 days, depending upon the temperature. Larvae feed, become fully grown in 2 to 4 weeks, and pupate. First- generation adults emerge 1 to 2 weeks after pupation (late June or early July). A complete life cycle requires from 6 to 9 weeks. This insect has two, and sometimes three generations per year.
A few adults can usually be found on peanuts in late June, although heavy infestations do not occur until the third or fourth week in July. The greatest adult populations are usually found during late July and early August, when second-generation egg laying occurs. In late fall, these last adults assemble on weeds, alfalfa, or clover where they spend the winter.