mate soon after emergence. Western corn rootworm females need to feed for about two weeks before they can lay eggs. Temperature and food quality influence the pre-oviposition period. Females typically lay eggs in the top of soil, although they may be laid more than deep, particularly if the soil surface is dry. Western corn rootworm females are more likely to lay some of their eggs below the depth than northern corn rootworm females. Feeding habits Rootworm larvae can complete development only on corn and a few other species of grasses. Rootworm larvae reared on other grasses (specifically, yellow foxtail) emerged as adults later and had smaller head capsule size as adults compared to larvae reared on corn. Adults feed primarily on corn silk, pollen and kernels on exposed ear tips, although they will feed on leaves and pollen of other plants. Adults begin emerging before corn reproductive tissues are present, adults may feed on leaf tissue, scraping away the green surface tissue and leaving a window-pane appearance. However, adults quickly shift to preferred green silks and pollen as they become available. Northern corn rootworm adults feed on reproductive tissues of the corn plant, but rarely feed on corn leaves. "Northern" adults are more likely than "western" adults to abandon corn and seek pollen or flowers of other plants as corn matures. Feeding damage Most of the damage to corn is caused by larval feeding. Hatchlings locate roots and begin feeding on the fine root hairs, burrowing into root tips. As larvae grow, they feed on and tunnel into primary roots. When rootworms are abundant, larval feeding and deterioration of injured roots by root rot pathogens can result in roots being pruned to the stalk base. Severe root injury interferes with the roots' ability to transport water and nutrients, reduces growth and results in reduced grain production. Severe root injury may result in lodging of corn plants, making harvest more difficult. Silk feeding by adults can result in pruning at the ear tip, commonly called silk clipping. In field corn, beetle populations are occasionally high enough to cause severe silk clipping during pollen shed, which may interfere with pollination. History of invasions The Western corn rootworm rapidly expanded its range in North America during the second part of the 20th century. It is now present from the southwestern region of the US Corn Belt to the east coast. It was introduced