Annual Wheat Stem Sawfly Survey- CO
Each year, our lab surveys 15+ Colorado counties for sawfly infestation. This data is then used to monitor sawfly movement and provide a database for use in future projects. See the image below for our recent survey results.
2025 Wheat stem sawfly infestation in Colorado. Image credit: Adam Osterholzer
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This graphic can be downloaded here:
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Annual Wheat Stem Sawfly Survey- KS
Our team has recently begun sampling Kansas for infestation. See the image below for our most recent results.
2025 Wheat stem sawfly infestation in Kansas. Image credit: Adam Osterholzer
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This graphic can be downloaded here:
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Wheat Stem Sawfly Flight Timing
We conduct sweeps to track the timing of when adult sawflies emerge and target wheat crops. This data helps us predict future flights.
Graphic depicting WSS flight data 2021-2025. Updated by Ana de Zoten and Adam Osterholzer.
Solid Stem Assessment Screening
Breeding wheat to have semi-solid stems remains the main control measure for mitigating sawfly damage. Increasing the stem solidity makes it more difficult for sawflies to lay their eggs. Semi-solid stems are also less suitable for larvae to develop in than hollow stems.
We cooperate with Dr. Esten Mason of the CSU Wheat Breeding and Genetics Program to help further this research. We screen stem solidity for a variety of experimental lines. This data is utilized to predict a line's resiliency to sawfly infestation. It can also be used to determine how environmental conditions impact solid stem gene expression.
We cooperate with Dr. Esten Mason of the CSU Wheat Breeding and Genetics Program to help further this research. We screen stem solidity for a variety of experimental lines. This data is utilized to predict a line's resiliency to sawfly infestation. It can also be used to determine how environmental conditions impact solid stem gene expression.
Parasitoid Wasp Studies
Bracon wasps are parasitoids and a potential control measure for sawflies. These insects will seek out sawfly larvae feeding within wheat stems. After paralyzing the larva, the parasitoid lays its own egg inside the stem. The offspring consumes the sawfly larva, killing it before it becomes an adult.
2025 was the first year our program found significant Bracon populations during our statewide survey. The map below displays WSS infestation in the blue-to-red color scale. Percentages of Bracon parasitism are overlaid on top of it with triangle graphics. We hope to see these Bracon populations increase in upcoming seasons. These insects are effective against WSS in other states but have not yet established in CO wheat fields.
Our program is currently attempting to supplement native parasitoid populations with specimens from Nebraska. This initiative is being undertaken in partnership with Colorado Wheat, USDA-ARS, and the University of Nebraska-Lincoln. The preliminary results look promising, with large numbers of Bracon surviving the transportation process.
2025 was the first year our program found significant Bracon populations during our statewide survey. The map below displays WSS infestation in the blue-to-red color scale. Percentages of Bracon parasitism are overlaid on top of it with triangle graphics. We hope to see these Bracon populations increase in upcoming seasons. These insects are effective against WSS in other states but have not yet established in CO wheat fields.
Our program is currently attempting to supplement native parasitoid populations with specimens from Nebraska. This initiative is being undertaken in partnership with Colorado Wheat, USDA-ARS, and the University of Nebraska-Lincoln. The preliminary results look promising, with large numbers of Bracon surviving the transportation process.
2025 Sawfly infestation and subsequent parasitism. Image credit: Adam Osterholzer
Ancestral Wheat Screening
We screen for novel sources of resistance to sawflies in ancestral wheatgrasses. Breeding programs are utilized to incorporate these resistances into commercially viable wheat. We test for sawfly resistance by deliberately exposing plants to adult sawflies in the field. By evaluating the oviposition and larval survival data, we determine whether resistance has been achieved. We partner with the Wheat Genetics Resource Center at Kansas State University on this project.
Unloading experimental lines for sawfly exposure.
Image credit: Henrique Vieira
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Sawfly infesting experimental lines.
Image credit: Henrique Vieira
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Evaluating Use of Fusarium spp. Fungi in Sawfly Control
We have observed strains of Fusarium spp. fungi naturally infesting sawfly in Colorado. While Fusarium is a common plant pathogen, these strains appear to only be only harming the insect larvae. Field samples were taken to the lab for efficacy trials.
Our initial results look promising, with three isolates causing rapid larval mortality. Greenhouse and field trials are being prepared to test the isolates in real-world conditions. We hope to provide growers with a treatment that could be applied to WSS infested wheat on a commercial scale.
Our initial results look promising, with three isolates causing rapid larval mortality. Greenhouse and field trials are being prepared to test the isolates in real-world conditions. We hope to provide growers with a treatment that could be applied to WSS infested wheat on a commercial scale.
Progression of fungal infection in a WSS larva. Image credit: Venkatesh Padimi.
Graph depicting WSS % mortality after larvae were exposed to a fungal isolate. Image credit: Venkatesh Padimi.
Degree Day Model for Predicting Sawfly Emergence
Our Ph.D student Henrique Vieira conducted this research. CoAgMet weather data was used with historical sawfly infestation to help growers predict sawfly flights. Based upon Henrique's model, we predict that sawflies will begin emerging at 148 growing degree days (GDD). Growers can expect the most adults at 224 GDD, followed by severe decline at 354 GDD.
We recommend scouting stubble for sawfly infestation (looking for stubs, cutting open stems to find larvae, etc.) prior to 148 growing degree days. This will let growers see if sawflies will emerge and infest their nearby wheat fields. Growers can monitor GDD accumulation at: pnwpest.org/cgi-bin/ddmodel.us?spp=aaa&uco=1
We recommend scouting stubble for sawfly infestation (looking for stubs, cutting open stems to find larvae, etc.) prior to 148 growing degree days. This will let growers see if sawflies will emerge and infest their nearby wheat fields. Growers can monitor GDD accumulation at: pnwpest.org/cgi-bin/ddmodel.us?spp=aaa&uco=1
Graphic depicting the relationship between growing degree day accumulation and WSS abundance. (Vieira et al., PLOS One)
