Western Corn Rootworm

Diabrotica virgifera virgifera

Western corn rootworm adult feeding on corn silks
Western corn rootworm adult feeding on corn silks. Photo courtesy of the Agricultural Research Service.
Western corn rootworms are an extremely destructive pest of corn in the U.S., particulary since they attack corn both as larvae and adults.
The western corn rootworm adult is approximately 1/4" in length and has a yellow-green body with distinct black strips which distinguish it from the related northern and southern corn rootworm species.
Photo of adult southern, northern, and western corn rootworms
Photo of adult southern, northern, and western corn rootworms. Photo courtesy of R.L. Croissant. Licensed under CC BY 3.0.
The larva are thin and grow up to 1/2" long. They have a brown head and white body.
Western corn rootworm larva
Western corn rootworm larva. Photo courtesy of Scott Bauer. Licensed under CC BY 3.0.
Larvae feed on the roots of corn plants, reducing their ability to absorb water and nutrients which can result in significant yield loss, particularly in dry conditions. The weakened roots can also make the plants prone to lodging making harvest more difficult.
Adults feed on corn silks, reducing polination and hence the total number of kernels, resulting in significant yield loss. Adults may also feed on the leaves.
Soil applied insectides at planting can be effective at controlling western corn rootworm. Seed treatments can also provide control for low to moderate infestations. Always read and follow all label instructions.
Many Bt traits provide protection against western corn rootworm.
Because western corn rootworms can only complete their lifecycle on corn (and related grasses), crop rotation was once an effective control technique. However, some western corn rootworms adults now bypass this technique by laying eggs on soybeans (so that the larva which hatch the following year are likely to be in a corn field). Nonetheless, fields with high adult pressure one year will likely have high larval pressure the following year and so rotating away from corn in these fields remains a good management strategy.