Corn Rootworm Identification
Corn rootworm belongs to the Chrysomelidae (leaf beetle) family of beetles. The western and northern corn rootworm species cause significant economic injury to corn in much of North America. Southern corn rootworm is also a pest of corn, though it is less severe and rarely causes economic loss in the major corn-producing states. It is impossible to distinguish the egg and larval stages of each species in the field, but adults can be easily identified.
Eggs are oval, creamy-white in color, and less than 1/32 inches long. Larvae are slender, less than ½ inch long, and white with a dark brown head. They are known for their double-headed appearance because of a dark plate on the top of the tail section. Pupae are white but otherwise resemble the adult.
Western corn rootworm
The western corn rootworm (WCR) adult is ¼ inch long and has a yellow body with three black stripes that do not extend to the tip of the abdomen. Male and female WCR can often be distinguished by the striping on their wings: females generally have distinct stripes while males can look like a black smudge. However, sexes for all corn rootworm species can be distinguished by looking at the apex of the abdomen: females’ are pointed, while males’ are blunt.
Be aware of look-alikes! The striped cucumber beetle is often confused with western corn rootworm. These two species have several ecological differences (timing of adult activity and food preferences), but they look similar. The striped cucumber beetle, however, has more rigid stripes that extend to the tip of the abdomen. They are also black on the underside of the body (compared to yellow for WCR) and have yellow legs (compared to black for WCR).
Northern corn rootworm
The northern corn rootworm (NCR) adult is ¼ inch long and generally light green with no distinct markings. Beetles may be tan in color when newly emerged. Northern corn rootworm sexes cannot be distinguished based on color or pattern.
Be aware of look-alikes! The green adult northern corn rootworm is not often confused with other insects in corn or soybean fields, but the tan/yellow morph may be confused with colaspis beetles. Grape colaspis and Iowa colaspis (in Iowa and Nebraska) beetles are much smaller than NCR (max. 1/6 inch long). Both species appear striped due to longitudinal pits on the elytra. Iowa colaspis has four complete stripes on each wing while grape colaspis has eight stripes. Northern corn rootworm does not have stripes.
Southern corn rootworm
The adult southern corn rootworm (SCR; also spotted cucumber beetle) is 3/8 inch long and yellow to light green in color with a black head, antennae, and legs. Their forewings have 12 black spots arranged in 3 rows of 4 spots.
Be aware of look-alikes! The bean leaf beetle is often confused with southern corn rootworm, especially because both can be found feeding in soybean. Of the corn rootworm species, SCR is most likely to feed on other food resources and can often be found in soybean or cucurbit crops (squash, melons, pumpkins, etc.). Bean leaf beetle usually has 4 black spots on the elytra, but may have two or none, and is distinguished by the black triangle on the back just above the spots.