Publication E-49
January 1977
Purdue University
Cooperative Extension Service
West Lafayette, Indiana 47907

Soil Insects Affecting Corn
David L. Matthew, Jr. and C. Richard Edwards, Extension Entomologists
Several kinds of insects spend a part of their life cycle in the soil of corn fields.
The larvae feed on the seeds and roots of corn plants causing a reduction in stand, loss of plant vigor, lodging and sometimes death of plants. Low insect populations are seldom noticed; any effect they might have on plants would be considered non-economic -- and control applications not profitable. However, damaging infestations of soil insects can develop within an area of a corn field or be present in an entire field. These soil insects have been collectively referred to as the "soil insect complex" that includes the corn rootworms, wireworms, cutworms, white grubs, sod webworms, seed beetles, seed maggots and billbugs. Although once considered extremely damaging and a serious threat to corn production in many fields, the severity of damage caused by the "soil insect complex" is much less today than 10 to 15 years ago.

CORN ROOTWORMS
Three species of corn rootworms are commonly found in Indiana. These include the southern, northern, and the western corn rootworm.

Rootworms are small, thread-like, whitish larvae about 1/2 inch long which later develop into beetles. They have a brownish head and tail section, and six tiny legs near the head end of the body. Rootworms consume small rootlets and tunnel inside the larger primary and brace roots. The northern and western species overwinter as eggs in the soil and develop on the roots of corn (rarely on other grasses). The probability of damage increases where corn is grown continuously on the same land.
Infested plants may lodge and later grow up in a curved "sled-runner" or "gooseneck" shape. Root damage occurs from late May until mid July. When full grown, the root-worms pupate and later emerge from the soil as 1/4 inch long green, spotted or striped beetles.

The western corn rootworm is now established in most counties in the northern two-thirds of the State.

Figure 1. Shaded area is infested with western corn rootworm.
* First beetles collected in 1976.

Cooperative Extension Work in Agriculture and Home Economics, State of Indiana, Purdue University and U. S. Department of Agriculture Cooperating. H.G. Diesslin, Director, West Lafayette, Ind. Issued in furtherance of the furtherance of the Acts of May 8 and June 30, 1914. It is the policy of the Cooperative Extension Service of Purdue University that all persons shall have equal opportunity and access its programs and facilities without regard to race, religion, color, sex, or national origin.