Grape colaspis – Colaspis brunnea (Fabricius), Chrysomelidae, Coleoptera
Adult – The oval, yellowish-brown beetle is 4 to 5 mm long. The wing covers appear striped due to the presence of longitudinal rows of shallow indentations.
Egg – The smooth, white to yellow egg is about 0.6 by 0.25 mm.
Larva – Measuring up to 7 mm long, the grayish-white or tan larva has a dark brown head and prothoracic shield. It is stout and grub-like in form with three pairs of legs near its head and fleshy appendages on the abdominal segments.
Pupa – Whitish at first, the 4 mm-long pupa gradually darkens.
Grape colaspis passes the winter in the soil as a grub (larva) from the previous season. Typically, the adults will only lay eggs in legume plantings (e.g. soybean) during the previous season and, therefore, if current year soybean seedlings are to have a problem, they must follow last year’s soybean crop. Rotation eliminates grape colaspis problems. After overwintering below the plow layer, grape colaspis grubs move near the surface in later May and feed on seedling roots. The grubs are small (to 5⁄16 inch), “C” shaped, white larvae with a brown head capsule and neck shield. Damaged seedlings have few lateral roots and the underground stem may show feeding on the bark. Seedlings may die or be stunted from the feeding. This insect will almost always be restricted to spots in the field and is most abundant on organic soils. Grape colaspis damage is often wrongly interpreted as nematode damage; however, it can be identified by the characteristic root and stem feeding signs. Often the presence of small, light brown adult beetles (less than 1⁄4 inch) feeding in the plant terminals will aid problem identification. There is no remedial treatment. Replanted soybeans are seldom attacked since the larva responsible for the original injury will have transformed into beetles and emerged. Foliage feeding by the emerged adults is insignificant.
Publication date: March 17, 2020
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