Abstract
Historically, the wheat stem sawfly, Cephus cinctus Norton was a pest in spring wheat-growing regions of the northern Great Plains. However, in the 1980s, it was found infesting winter wheat fields in Montana. Infestations were first detected in western Nebraska in the 1990s, and have since spread throughout the Nebraska Panhandle. Larval damage occurs from stem-mining, but stem girdling that results in lodged stems that are not harvested results in the greatest yield losses. The biology and phenology of the wheat stem sawfly are well described in the northern portion of its range, but they are lacking in Colorado, southeast Wyoming, and Nebraska. In this study, the phenology and dispersal of the wheat stem sawfly in Nebraska winter wheat fields is described using sweep net and larval sampling. During this 2-yr study, adult activity began on May 23 and ended on June 21. Adult sex ratios were 2.32 males per female in 2014 and 0.46 males per female in 2015. Both sexes demonstrated an edge effect within the wheat fields, with greater densities near the field edge. The edge effect was stronger for male wheat stem sawfly than females. Wheat stem sawfly larval density also had an edge effect, regardless of the density of female wheat stem sawfly present. This information will be useful for developing management plans for the wheat stem sawfly in Nebraska and neighboring regions.
Highlights
Upon emergence in the spring, female wheat stem sawfly disperse in search of hosts
In 2014, the first wheat stem sawfly were sweep net sampled on May 14, and the last wheat stem sawfly were sampled on June 27
In 2015, the first wheat stem sawfly were sampled on May 12, and the last wheat stem sawfly were caught on June 25
Summary
Upon emergence in the spring, female wheat stem sawfly disperse in search of hosts. The lifespan of an adult wheat stem sawfly is about. Solid stem varieties crush wheat stem sawfly eggs, increase desiccation, inhibit larval movement, and result in less fecund females emerging (Holmes and Peterson 1961, 1962; Cárcamo et al 2005). This edge effect continued to decline up to 90 m into the field (Goosey 1999, Morrill et al 2001, Weaver et al 2004) These studies often combined male and female wheat stem sawfly for analysis. It may be practical to present wheat stem sawfly densities in aggregate, but it is the females that are ovipositing in wheat stems. Goosey (1999) and Sing (2002) analyzed wheat stem sawfly dispersal into wheat separately for each sex. Sing (2002) found that female densities do not decline as dramatically as male densities farther into the wheat field
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