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Adult Description: The Hessian Fly (Mayetiola destructor) adult is tiny, fragile, and mosquito-like. It measures 1/8 inches, and adults are gray, with fragile appearing appendages. For this reason, they are commonly compared to mosquitoes. Adults live about 3 days.
Larva Description: Immature forms are white legless maggots. Maggots work their way down the groves in leaves. Next, they rasp on the stem and suck up the sap that oozes from the wound. They do not move once feeding has begun. After about two weeks of feeding, their outer skin loosens, turns brown and hardens forming the protective case often called the "flax seed". It is this stage that is most often seen by producers and scouts. Out of this "flax seed" emerges the adult to begin the cycle over again.
Host Plant: Wheat (spring and winter) is the preferred host of the Hessian fly. Barley, oats, triticale and rye are generally considered resistant. Wild grasses such as quackgrass, western wheatgrass, rye grasses are also known hosts.
Maggots are the only stage that damages wheat since the adults do not feed. A single maggot feeding on a plant for three days can stunt a young plant or tiller. In the fall, maggots usually feed on the lower leaves and can cause heavy damage. Infested plants become stunted and stiffly erect, and leaves are thickened with a bluish green color. Heavily damaged plants usually die during the winter. Plants damaged during the spring have similar symptoms to those damaged in the fall; however, heavy parasitism (more than 95 percent) usually limits damage during the spring. As the seed heads begin to fill, heavily infested plants will lodge, and yields can decline by at least 16 bushels per acre.
There appears to be a spring and a fall generation. For winter wheat, the fly invades fields in September and establishes a fall generation. A second generation occurs the next spring. The insect survives the summer as a 4th instar larva in the "flaxseed" stage in infested wheat stubble. This shiny-brown, seed-like puparium can be found at the base of old plant crowns. It may also occur in straw, near the nodes, behind the leaf sheaths.
Rain will trigger fly emergence in early September. Farmers who plant winter wheat early will have young wheat in the seedling stage when the flies emerge. The potential for infestation and damage to sensitive, young plants is high.
The reddish, 1st-instar larvae move from empty egg shells and crawls downward, gradually reaching the base of the leaf. Here, between the leaf and tiller, the young larva begins to feed, with its head in a downward position.
A single larva, feeding for just 3 days, is capable of stunting a young wheat plant or tiller. The larvae feed for about 2-3 weeks. They then form the puparium that resembles a "flaxseed". The non-feeding 4th-instar larva overwinters within this structure.
Some mortality occurs each winter depending on many factors, including: temperature, moisture, and natural enemies. In the spring, development resumes and the larva transforms into a pupa, still inside the puparium. The spring emergence of adult flies follows within a few days. The adult life is short, lasting an average of only 2-3 days.
This insect probably originated in the southern Caucasus region of Russia or Asia, and was accidentally introduced into North America when Hessian troops imported straw bedding during the American Revolutionary War. Hessian flies were first observed on Long Island, New York around 1779. Today, they are present in most wheat-growing areas of the United States, and can be found coast-to-coast. It has also been classified as a worldwide pest as well. In 1836 a severe infestation of Hessian flies resulted in a crop shortage aggravating the financial problems of farmers leading up to the Panic of 1837.
U.S. Habitat: Hessian flies establish themselves withing wheat and other cropfields.
U.S. Present: Since the Hessian fly was introduced during the Revolutionary War, it has established itself in most of the U.S.
Texas: The Hessian Fly has successfully established in Texas. Although most eastern counties are affected, a few counties in west Texas may remain uninfected.
Mosquito-like in appearance. Also resembles other midges.
Since control is based entirely on prevention if a field becomes infested, control measure may not be effective. Management practices to reduce economic losses include:
- Grow adapted wheat varieties that have genetic Hessian fly resistance. Check with the county Extension agent for resistant varieties adapted for your area.
-Plant wheat later in the fall (mid-November) to avoid fall generations.
-Deeply bury crop residue to reduce population numbers.
-Rotate crop types in individual fields to help reduce pest numbers.
-Do not move infested straw from an infested area to an uninfested area.
Under Texas conditions, insecticide treatments may not give economical or practical control of the Hessian fly.
Hatchett, J. H., and R. L. Gallun. (1968). Frequency of Hessian Fly, Mayetiola destructor, Races in Field Populations. Annals of the Entomological Society of America. 61 (6) 1446-1449.
Lamiri, A., S. Lhaloui, B. Benjilali, M. Berrada. (2001). Insecticidal Effects of Essential Oils Against Hessian Fly, Mayetiola destructor (Say). 71 (1) 9-15.
McKay, P. A., J. H. Hatchett. (1984). Mating Behavior and Evidence of a Female Sex Pheromone in the Hessian Fly, Mayetiola destructor (Say) (Diptera: Cecidomyiidae). 77 (5) 616-620.