Rootworm

'Rootworm' most commonly refers to the larvae of beetles in the genus Diabrotica, particularly the western corn rootworm, Diabrotica virgifera, and the northern corn rootworm, Diabrotica barberi, both native to North America and among the most economically significant below-ground pests of corn on the continent. Adult Diabrotica beetles are small, often greenish or striped, and are frequently seen feeding on corn silks, pollen, and leaves above ground, while the larvae live and feed entirely underground.

The larval stage is the more damaging phase for corn production, as the slender white grubs feed directly on root tissue, tunneling through and pruning roots as the plant develops. This root damage can affect a plant's ability to take up water and nutrients and, in some cases, to remain firmly anchored in the soil.

Because corn rootworms have historically been closely tied to continuous corn cultivation, their biology and population cycles have been extensively studied, and the group is considered one of the most significant below-ground insect challenges in North American corn-growing regions.

• Larva is slender, white to cream-colored, and worm-like, with a distinct light brown head capsule
• Reaches up to about 1.3 cm (0.5 in) in length at maturity
• Has three pairs of small legs near the head and a slightly darker plate on the last abdominal segment
• Found underground around plant roots rather than on foliage, making it far less commonly observed than the adult beetle
• Adult beetles associated with the larvae are small, roughly 6 mm long, and often yellow-green with black stripes or spots depending on species

Found in agricultural soils across the corn-growing regions of North America, particularly the Midwestern United States, wherever corn is planted, especially in fields with a history of continuous corn cultivation. Larvae are present in soil from late spring through mid-summer, feeding on developing root systems.

Larvae live entirely within the soil, feeding on and tunneling through the root systems of host plants, primarily corn, though some species also affect the roots of other grasses and, less commonly, related crops. This underground feeding can prune root mass as the plant grows. Adult beetles that develop from these larvae emerge later in the season and feed above ground on corn silks, pollen, and leaves, as well as flowers and foliage of cucurbit crops in some species, linking the below-ground larval stage to more visible above-ground adult activity.

Adult beetles lay eggs in soil near the base of host plants in late summer, and the eggs overwinter in the soil. Larvae hatch the following late spring as soil warms and host plant roots become available, feeding and passing through three instars over several weeks. Mature larvae form a small earthen cell in the soil and pupate, emerging as adult beetles in mid to late summer. One generation is typically completed per year in most of the range.