Southern Corn Rootworm
(Spotted Cucumber Beetle)
Diabrotica undecimpunctata howardi (Barber), Chrysomelidae, COLEOPTERA


Adult - The adult beetle is about 6 mm long with a bright yellowish-green body. The head, legs, and antennae are black, and twelve black spots are present on the wings. Color plate.

Egg - The egg is dull yellow, oval, and about 0.6 mm long (the size of a pinhead).

Larva - The fully grown larva is 15 to 16 mm long with a yellowish-white, somewhat wrinkled body. It has six tiny brownish legs.

Pupa - White to yellow in color, the pupa is about 6 mm long.


Distribution - The southern corn rootworm is widely distributed, occurring in most areas east of the Rocky Mountains, in southern Canada, and in Mexico. It is most abundant and destructive in the southern states.

Host Plants - Southern corn rootworm larvae infest the roots of many grass crops and weeds as well as those of peanuts, alfalfa, and occasionally cucurbits. They are most damaging to corn and peanuts. The beetles are general feeders on at least 280 plant species, including most cultivated crops. They prefer broad-leaved hosts, especially cucurbits, and are particularly attracted to flowers.

Damage - The southern corn rootworm prefers moist soil and is most injurious to corn during cold, wet springs. Corn is most likely to be injured if it is under no-till culture, in a continuous rotation, or following turned-under winter legumes. Both the adults and larvae damage corn, but the larvae are more destructive. Color plate.

Larval cause corn injury in the spring. They chew out round holes (0.75 mm in diameter) through the growing points, killing the terminal blades. Stands may be reduced 50 to 90 percent or more. Extensive feeding on the roots may occur late in the season. Plants with severe root damage lodge during wind and rain storms, often causing the stalks to "goose neck" and making harvest more difficult. In addition to direct injury, rootworms transmit bacterial wilt disease from infested plants to healthy plants and make wounds that allow the entry of rot organisms.

Although the larvae cause most of the injury to corn, the adults feed upon every part of the plant above ground. Most damaging is their feeding on newly emerging, unpollinated silks causing sparsely filled ears. The beetles also carry the bacterial wilt organism, but plants are more often inoculated by contaminated larvae.

Life History -The beetles overwinter in any kind of vegetative cover, though they prefer the bases of plants that have not been killed by frost. In southern states, the adults first become active about the middle of March and lay eggs from late April to early June. Eggs are laid singly, each female producing as many as 500. They hatch in 7 to 10 days, depending on the temperature. The larvae feed for 2 to 4 weeks before pupating. First-generation adults emerge from late June to early July in the southern states. A complete life cycle requires from 6 to 9 weeks.

In the southern states, including North Carolina, there are two, and sometimes three, generations per year. In areas where there are multiple generations, the larvae of first-generation eggs are found on the roots of corn from late spring until mid-summer. Second- generation adults are found from September to November. These 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.


Both cultural and chemical methods are used to control rootworms. In the South, the following cultural practices reduce the southern corn rootworm population. First, early plowing and/or disking at least 30 days before planting corn removes vegetation and discourages further egg-laying. Second, early planting and seeding rates near the maximum for the variety ensure a good stand. Finally, carrying out recommended agronomic practices ensures vigorous plants with improved tolerance.

Preemergence granular insecticides have been very successful in the control of southern corn rootworms. In North Carolina corn or sorghum crops, it is not currently economically feasible to control the larvae by spraying the adults. For further control information, consult the current North Carolina Agricultural Chemicals Manual.