Jeff Bradshaw

PREVALENT PEST: A Nebraska survey found all dominant grass species had some level of infestation of stem sawfly, along with some level of sawfly parasitism.

Parasitoid wasp still the most effective control for wheat stem sawfly in Nebraska.

Jan 15, 2019

By Jeff Bradshaw and Bethany Bergstrom

Nebraska Extension has conducted a wheat stem sawfly survey for several years. The sawfly survey was discontinued in 2017; however, data from the survey are being used strategically for grassland and on-farm evaluation of sawfly-parasitoid relationships.

Extension is conducting a survey and landscape analysis to better understand the ecology of both the wheat stem sawfly and its parasitoid in Nebraska. The parasitoid wasp that attacks sawfly larvae in wheat stems is currently the most effective control method for the wheat stem sawfly in Nebraska.

Because the wheat stem sawfly is native to North America, it infests many grasses (not just wheat). Because parasitoid-sawfly relationships may have had more time to co-evolve in a native setting (e.g., the Nebraska Sandhills), the survey is conducting transects that span both wheatland and grassland regions. In both regions, Extension is surveying grassland species from borrow pits to rangeland to seek out both sawflies and sawfly parasitoids.

Extension is collecting sweep net samples and stem samples through the survey range to better understand the role of grasslands in sustaining or regulating sawfly populations. However, the focus is on identifying plants and habitats that may encourage greater conservation of sawfly parasitoids and biological control mechanisms.

Results so far have found:

  • Some of the most dominant grassland plants in the survey are crested wheatgrass, intermediate wheatgrass, needle and thread, sand dropseed, and smooth brome.
  • All dominant grass species had some level of infestation of stem sawfly (Table 1). Smooth brome had the highest infestation level (average of 43.4%).
  • All dominant grass species had some level of sawfly parasitism. The highest proportion of sawfly parasitism was found in intermediate wheatgrass (about 19%).
  • Further analysis is underway to relate findings in grasslands to wheatland.
Table 1. Dominant grass species sampled from grassland habitats for wheat stem sawfly and sawfly parasitoids in 2018 (n = 32
Source: UNL CropWatch

Bradshaw is an Extension entomologist, and Bergstrom is a University of Nebraska-Lincoln entomology graduate student. This report comes from UNL CropWatch, which is solely responsible for the information provided and is wholly owned by the source. Informa Business Media and all its subsidiaries are not responsible for any of the content contained in this information asset.