Cereal leaf beetles were first detected in the United States in Michigan in 1962. This insect species can now be found throughout the eastern United States and southern Canada. At the moment, cereal leaf beetle larvae are numerous in some southern Illinois wheat fields. Of greatest concern is injury to flag leaves. If you've not monitored wheat fields for this insect pest, don't delay your scouting trip! Although cereal leaf beetles are primarily considered of economic importance in wheat, both adults and larvae may feed on oats, barley, rye, and corn. Adult cereal leaf beetles typically consume the shoots of grain plants; however, the "slug-like" larvae concentrate on leaf tissue between veins. Injured plants may take on a silvery sheen. |
Cereal leaf beetle adult.
Adult cereal leaf beetles (3/16 inch in length) are primarily metallic blue (head and wing covers) with red-orange legs. The prothorax (body segment just behind the head) also is red-orange. Adults overwinter beneath plant debris, and during the spring they occupy their time by feeding on uncultivated grass species. Later in the spring they begin to move into cultivated fields. Adult cereal leaf beetles feed for about 2 weeks before they begin laying eggs. Eggs hatch in about 5 days, and larvae usually require 10 days to become fully grown. After the larvae finish feeding, they move to the ground, pupate in the soil, and emerge as adults after 2 to 3 weeks. Following emergence, adults feed briefly, then aestivate until cooler soil temperatures return in the fall. Fall activity by adults consists of locating suitable overwintering shelter. In all, the annual one-generation life cycle requires about 45 days.
Recently deposited eggs are elliptical, yellow, and smaller than a pinhead. Just before hatching, they turn almost black. Eggs are deposited singly or in rows of three or four but never in clusters. They are usually found close to the mid-rib on the upper surface of a leaf. The larva resembles a slug or a small glob of mud. This moving "glob" is actually an accumulation of fecal matter carried around by the larva. This unusual behavior is probably a defensive mechanism that discourages most predators and parasitoids from attacking the larval stage of this pest. However, at least three parasitic wasps use cereal leaf beetle larvae as hosts.
The potential for yield loss depends on the growth stage of wheat plants, the location of feeding injury on wheat plants, and the density of the pest. Severe injury to the flag leaf can reduce yields by 25% to 30%. An insecticide treatment may be justified when the combination of eggs and larvae averages three or more per stem. An older treatment guideline suggested that an insecticide might be warranted when one or more larvae is present per flag leaf. Products labeled for use against cereal leaf beetles in wheat include Sevin XLR Plus (1 qt) and *Warrior T or 1E (2.56 to 3.84 oz). Those products preceded by an asterisk are restricted for use and may be used only by certified applicators.--Mike Gray and Kevin Steffey