NPIPM:Colaspis beetles (soybean)
Authors: Buyung Hadi, Jeffrey Bradshaw, Ken Ostlie
Colaspis beetles are commonly found in the eastern half of the USA, but their range extends westward into Arizona and New Mexico. The grape colaspis, Colaspis brunnea, is the common species found on soybean and corn. Another colaspis beetle morphologically distinct from the grape colaspis, the Iowa colaspis, Colaspis crinicornis, has been reported from western Iowa and eastern Nebraska.
Identification
Adult grape colaspis beetles are small (about 1/6 in. or between 4-5 mm), clay-orange in color with tan stripes of punctures on each wing cover (elytron). Adult grape colaspis is smaller than Iowa colaspis. Additionally, adult grape colaspis has eight tan stripes on each wing cover while adult Iowa colaspis has around four complete stripes and one partial stripe on each wing cover.
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The eggs are found in the soil, white to yellow in color.
The larval stage of colaspis beetles is a white thick-bodied grub, 1/8 to 1/6 in. (3.2-4.2 mm) in length. The head and neck-shield are harder then the remaining body parts, both are whitish when newly hatched but soon turn brownish or reddish. The underside of the larval body has many fine hairs. The larvae somewhat resemble white grub of scarab beetles but colaspis beetle larvae are much smaller in size. Colaspis beetle larvae live underground, feeding on roots.
The pupae are found in the soil encased in earthen cells. They are about 1/8 in. (3.2 mm) in length, white in color except for the eyes and mandibles, which are red and black, respectively, at larval maturity.
Life Cycle and Seasonal History
In the Northern Plains, colaspis beetles are univoltine, producing one generation of beetles per year. The beetles overwinter as early instar larvae underground. The larvae become active between spring and summer. The adults emerge from the soil between June and July. In midsummer, the adult beetles mate and lay eggs in the soil, around the host root system. In about two weeks the eggs hatch, begin feeding, and the larvae remain underground throughout winter.
Plant Injury and Damage
Colaspis beetle larvae feed on corn and soybean roots. The economic impact of corn root feeding apparently is more severe than soybean root feeding. Because colaspis beetles can survive on both corn and soybean, crop rotation between corn and soybean may have limited benefit in controlling colaspis beetle populations or this practice may increase colaspis abundance over time. No studies has verified the impact of this cultural practice on colaspis beetle abundance.
Adult grape colaspis feed on the leaves of a wide range of plants; corn, soybean, grapes, strawberries, cowpeas, beans, clover, timothy grass, June grass, potatoes, and apples. Substantial injury to soybean leaflets is evidence when beetle populations are large. Adult grape colaspis can transmit Bean pod mosaic virus.
Management Approaches
Souting and Threshold
Economic damage of colaspis beetles on soybean has not been documented. In some areas colaspis beetles are regarded as secondary pests of corn due to severe stunting as the consequence of seedling root injury. However, the incidence of colaspis beetle-related damage seems sporadic. No economic threshold is available for colaspis beetles.
Other Online Resources
For information regarding labels of chemical control options, please visit Agrian.com
