By the 1980s, these insects cost Ontario corn growers millions of dollars each year in insecticide treatment costs and reduced crop yield. Both species are still present in Ontario. The most significant damage done to corn by rootworms is the result of the larvae feeding on corn plant roots. In severe infestations, the entire root system can be destroyed. Even when the injury is less severe, damaged root systems do not function properly.
Plants suffer from a lack of water and nutrients, and yields are reduced.
Lodged plants are difficult to harvest and harvest losses are likely to increase. In severe situations, the entire crop may be flattened and unharvestable. Crop rotation is the preferred method of control because rotation of corn with any other crop for one year almost eliminates the risk of rootworm damage. Adult rootworms lay their eggs almost exclusively in existing cornfields in late summer. The eggs lie dormant over the winter and hatch into small, white larvae in mid-June.