Issue No. 7, Article 4/May 9, 2008
Watch for Other Insect Pests of Wheat, Too
While scouting for armyworms in wheat fields, one should also be on the alert for other insect pests that show up about this time of year. We have received one report of a severe infestation of Hessian flies in a wheat field in southern Illinois, a report that I intend to follow up on next week. The Hessian fly usually is of little concern for most wheat growers because they plant varieties with resistance to it. However, Hessian flies are notorious for developing biotypes that can overcome the most widespread genes for resistance, so we should always be on the alert. Also, wheat growers have largely ignored fly-free dates when planting wheat during the fall in recent years. Wheat planted before the fly-free date in a given area is always more susceptible to infestation by Hessian flies and aphids.
Hessian fly larvae are glistening white, maggot-like, and small, about 1/6 inch long when fully grown. They can be found feeding beneath the leaf sheaths at the bases of plants and just above nodes. The maggots use their mouthparts to suck up plant juices. Injured plants become stunted, and larval feeding prevents normal elongation of internodes. Hessian fly injury reduces the quantity and quality of the grain. When the larvae finish feeding, the brown puparia develop in preparation for adult emergence.
Hessian fly maggot (right, glistening white) and puparium, or "flaxseed" (left, brown) at the base of a wheat plant, 2001. (Photo courtesy of Kevin Black, Growmark, Inc.).
Although no one has yet reported to us finding cereal leaf beetles, now is about the time they start to show up. We have no good photographs of cereal leaf beetle adults or larvae, so you might want to check out images on the Web. You will find that the adult beetle is colorfulmetallic blue-black head and wing covers, rust red legs and prothorax (segment just behind the head). The larva is slug-like, with brown-black head and legs and yellow-orange body. The color of the body, however, is often hidden by a dark glob of mucus and fecal matter, which is believed to repel predators (you think?).
Both larvae and adults feed on wheat foliage, though feeding by the adults usually is not economic. The larvae eat long strips of tissue from between the leaf veins, usually leaving only the transparent lower leaf surface tissue. Heavily damaged fields appear frosted.
In-depth information about armyworms, cereal leaf beetles, and Hessian flies as well as many other insect pests of small grains can be found in the Handbook of Small Grain Insects published by the Entomological Society of America, available from APS Press. This handbook is an excellent resource for anyone interested in the most current knowledge associated with insect management in wheat and other small grains.--Kevin Steffey