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The wheat stem sawfly, Cephus cinctus Norton (Hymenoptera: Cephidae), is a serious insect pest of wheat, Triticum aestivum L., in the northern central Great Plains. The sawfly has been a pest of wheat in Montana, North Dakota, and Canada since the early 20th century. It was first detected in Nebraska winter wheat in the early 1990s, in Scotts Bluff County. The sawfly has since spread throughout the Nebraska Panhandle region and become a pest of serious concern. To gain a better understanding of the sawfly in Nebraska, investigations on the emergence, dispersal, and sampling of the sawfly were conducted.
Observations on the emergence and dispersal of the adult sawfly were made in 2014 and 2015 in three winter wheat fields in the Nebraska Panhandle by using emergence cages, sticky traps, and sweep net sampling. Adult sawflies begin emerging in mid-May and are no longer found by the end of June. Adult sawfly densities decreased the farther into the wheat that was sampled. This edge effect was observed for both sexes of the sawfly, but it is more apparent with male sawflies.
The adult sawfly has an aggregated distribution when described by Taylor’s Power Law. By using Taylor’s Power Law, the number of sweep net samples required to maintain a desired precision level was determined. When sampling at early wheat heading, five, 20-sweep sweep net samples are needed to maintain a 20% precision level. These sampling data were correlated to larval infestation rates and used to develop a sampling plan that predicts larval infestation rates based upon stem density and the number of adults sampled. Sampling adults gives wheat growers ample time to take management action, such as swathing, during the current growing season. It also allows time for growers to change their wheat variety to a more resistant, solid stem wheat variety, for the next growing season.
Advisors: Jeffery D. Bradshaw and Gary L. Hein