Colaspis Beetles in Soybean

Crop Injury: Colaspis beetles (Colaspis spp.) are found in most soybean production areas of the U.S. Grape colaspis (Colaspis brunnea) is most common, but other colaspis species such as Iowa colaspis (Colaspis crinicornis) are found in some soybean production areas. Most economic injury is from larvae feeding on roots of plants soon after planting. Corn and rice are more vulnerable to root feeding than soybean. Damage often occurs in patches and can be confused with damage from nematodes and other cryptic root feeders. Adults are defoliators of soybean but are seldom numerous enough to cause economic levels of defoliation by themselves.

Pest Description: Adult beetles are clay-orange in color and are from ⅛ to 3/16 inch long. They have parallel tan lines on their forewings. The larvae are small, white grubs with visible legs and are up to 1/4 inch in length.

Colaspis beetle on soybean. Image: B. Kleinke.

Grape colaspis beetle. Image: Natalie Hummel, Louisiana State University AgCenter, Bugwood.org.

Life Cycle: Colaspis beetles overwinter as small larvae in the soil. In the spring, larvae feed on roots, sometimes causing economic damage to young plants of many species. Following pupation, adults emerge from the soil in mid-summer. Adults feed on a wide variety of crops, but seldom cause economic damage. Mating and egg-laying occurs within two weeks after emergence, and eggs take one to two weeks to hatch. Larvae feed on roots in the fall before overwintering begins again. One generation occurs each year throughout North America.

Scouting: Scouting is not generally recommended for colaspis beetle because the damage is caused by the larvae in the soil and there are no rescue treatments available after planting. Digging in the soil around plants to look for larvae can confirm an infestation. Using a sweep net after adult emergence in mid-summer can be used to select management options for the following year, but no thresholds are established. Dry soil conditions can exacerbate grape colaspis beetle injury.

Management: Economic injury from this pest is rare in most regions. When planting in fields with a history of colaspis beetle larval injury, use an insecticidal seed treatment and good agronomic practices to ensure that early plant root growth is vigorous. Crop rotations with cotton or rice may reduce damage to soybean, but corn is a suitable crop for colaspis beetle oviposition, so rotation between soybean and corn has not been shown to reduce populations.

Developed and reviewed by Fred Musser, Mississippi State University; Erin Hodgson, Iowa State University; and the Iowa State University Integrated Pest Management Program.

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