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The wheat stem sawfly is the most extensively studied insect pest of wheat in the northern Great Plains. The first comprehensive reviews were written by Criddle (1917) and Ainslie (1929). More recent reviews came from Drs. Bob Byers, Lou Wallace, and Harry McNeal. Extensive and thorough investigations of pest biology were conducted primarily in Alberta, Saskatchewan, North Dakota, and Montana. The results have contributed significantly toward our current understanding of the pest.
Adult sawflies appear briefly during May and June, and the original populations inhabited wild grasses. The first adults were obtained in 1890 in California. Even at that early date, their importance was anticipated. Riley and Marlatt predicted that: "The economic importance of this species arises from the fact that it may be expected to abandon its natural food source in favor of small grains, on which it can doubtless develop." Perhaps Riley and Marlatt were aware of other closely related sawfly species that infest wheat in the Old World. In 1896, sawflies were first detected in wheat in Souris, Manitoba; heavy infestations were found in 1907 near Minot, North Dakota. Damage was widespread in the state by 1910. Losses were estimated to be valued at $5 million in Manitoba and Saskatchewan in 1921. By 1926, sawfly damage was widespread and extensive with annual losses exceeding 25 million bushels in Montana and Canada. Surveys showed that sawflies occurred in grasses from the Peace River region of Alberta southward into New Mexico. However, early-maturing wheat fields in states south of Montana and the Dakotas avoided infestations.
Wheat production practices have influenced sawfly populations. Pioneers used horses when the prairies were first cultivated, and farmers grew oats for their feed. Oats are sawfly resistant therefore sawflies were suppressed in rotation systems which alternated between wheat and oats. The need for horses, and hence oats, was reduced after the advent of mechanized agriculture. As land committed to oats declined, sawfly survival was enhanced by the subsequent increase in wheat production.
Alternate-year summer fallow, with minimal or no tillage, began as a method for conserving soil moisture. Sawflies overwinter in wheat stubble, therefore the decline in heavy tillage improved sawfly, as well as parasitoid, survival. Establishment of narrow strip fields, oriented perpendicular to prevailing winds, reduced soil erosion but facilitated the sawflies' ability to infest neighboring crops.
One of the most significant contributions toward sawfly management was the development of solid-stemmed wheat. In 1934, Kemp obtained solid wheat from New Zealand, which was probably of Mediterranean origin. In 1938, Platt crossed this wheat with 'Apex', resulting in the variety 'Rescue' in 1946. Today, plant breeders at Montana State University continue to work towards improving solid stem varieties.
Changes in sawfly seasonal activity has occured over time. When first introduced, winter wheat avoided attack because of its early maturation while spring wheat was susceptible. By 1980, there were reports of severe damage in winter wheat in Montana. By 2000, sawfly emergence began nearly one month sooner than in the past. Late planted spring wheat commonly avoids attack because stem elongation does not occur until after the adult flight season is over. Because of this shift in emergence dates, the suggestions put forth in the 1945 Manual for Sawfly Control Workers in Alberta, (late seeding of spring wheat, trap strips to intercept adults, and use of resistant crops), are being revisited today in Montana.
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