Tag: Wheat stem sawfly

Week 16: Wheat Stem Sawfly

The wheat stem sawfly, Cephus cinctus, is native to western Canada. Its hosts include species of native grasses as well as rye, barley, and winter wheat. It is most economically damaging to spring wheat and durum wheat in western Canada.

**An adult wheat stem sawfly. Picture by Dylan Sjolie, AAFC-Saskatoon.**

Adult wheat stem sawfly do not feed; they live for about 10 days and spend that time mating, dispersing to wheat or durum crops, and laying eggs. Larvae are the damaging stage of the wheat stem sawfly life cycle. Larvae feed on pith inside the wheat stems. Because the larvae feed inside the wheat stems, the damage they cause is not obvious or easy to detect.

By feeding inside the host plant stems, wheat stem sawfly can reduce the quality and quantity of the grain produced by their host. In the late summer, the larvae also cut the stems of their host plant when they prepare to overwinter. The cut stems are susceptible to lodging.

In the fall, cut stems are used to estimate the density of wheat stem sawfly in wheat and durum fields using the protocol available from the Prairie Pest Monitoring Network. The results of the survey conducted in fall 2023 indicated that wheat stem sawfly densities were quite high in southern Alberta and south western Saskatchewan. Historical maps of the results of the wheat stem sawfly survey are also available from the PPMN Risk Maps page.

Additional information about the wheat stem sawfly is available from the Saskatchewan Ministry of Agriculture and from Alberta Agriculture and Irrigation. For more information, wheat stem sawfly was featured as an Insect of the Week in 2023 and is included in the Field Crop and Forage Pests and their Natural Enemies in Western Canada: Identification and Management field guide. (en français : Guide d’identification des ravageurs des grandes cultures et des cultures fourragères et de leurs ennemis naturels et mesures de lutte applicables à l’Ouest canadien).

Parasitoids of Wheat Stem Sawfly

Bracon cephi and Bracon lissogaster are the primary parasitoids that attack wheat stem sawfly and help to regulate wheat stem sawfly populations in North America. These closely related parasitoid species are described as idiobiont ectoparasitoids. The parasitoid larva, after hatching from an egg laid on the surface of the wheat stem sawfly larva, consume the entire host except for the host’s head capsule and exoskeleton. Both Bracon species complete their development and pupate inside the wheat stem. Their pupae are generally found inside the exoskeleton or beside the remnants of their consumed wheat stem sawfly host. There are two generations of B. cephi and B. lissogaster per year.  The first generation completes its lifecycle then exits the wheat stem to locate a new host to parasitize.  The second generation overwinters within the wheat stem.

**Adult *Bracon cephi* parasitoid, pictured inside a vial (hence the artistic effect!) by Dylan Sjolie, AAFC-Saskatoon.**

Bracon cephi and B. lissogaster are similar in appearance. The wasps are typically 2-15 mm long and brown in colour. They have a narrow waist connecting the abdomen to the thorax and the combined length of head plus thorax is equal to the length of the abdomen.  These parasitoid wasps have long antennae and two pairs of transparent wings. Females have a noticeable ovipositor protruding from the end of the abdomen.

Parasitoid population dynamics and efficacy are influenced by crop management practices. Parasitoids can be conserved by increasing the height of stubble when harvesting and reducing insecticide applications in grass ditches where natural enemies of the wheat stem sawfly are abundant.

For more pictures and information about the natural enemies of the wheat stem sawfly, check out our past Insect of the Week post about Bracon cephi!

Wheat Stem Sawfly

Native to North America, the wheat stem sawfly is an economic pest depending on spring and durum wheat as its main crop hosts. These insects also target winter wheat, rye, grain corn and barley, in addition to feeding on native grass species. It is interesting to note that wheat stem sawflies do not feed on oat crops, as oats are toxic to wheat stem sawfly.

Wheat stem sawfly larvae feed on pith inside the stems of their host plant. Their feeding activity affects crop yield and quality. As infested host plants mature, the larvae travel down the stem to its base, where “V” shaped notches are cut into the stem a little above ground level. These notches leave plants vulnerable to collapsing or lodging, especially during wind events. Because wheat stem sawflies also breed and develop on native grass species, economic damage tends to be most prevalent around crop margins where native and agricultural plants are found close together.

Adult wheat stem sawflies are 8–13 mm long with a wasp-like resemblance, due to their black body and yellow legs. Females have an egg-laying organ (an ovipositor) that extends from their abdomen. When resting on plant stems, these insects will point their heads downward. Mature larvae are 13 mm long and resemble whitish worms with brown heads.

Biological and monitoring information related to wheat stem sawflies in field crops can be found on our Monitoring Protocols page as well as on provincial Agriculture Ministry pages (Manitoba, Saskatchewan and Alberta). For more information, visit the wheat steam sawfly page in the Field Crop and Forage Pests and their Natural Enemies in Western Canada: Identification and Management field guide. (en français : Guide d’identification des ravageurs des grandes cultures et des cultures fourragères et de leurs ennemis naturels et mesures de lutte applicables à l’Ouest canadien).

2019 Risk and Forecast Maps for the Prairies

The 2019 Prairie-Wide Risk and Forecast Maps can be viewed and downloaded here.

Economically significant insect pests are monitored across the Canadian prairies each year, thanks to extensive networks of collaborators and cooperators. In 2018, that effort culminated in 5764 survey stops across Manitoba, Saskatchewan, Alberta and the BC Peace!

Here’s what’s included in the PDF file:

Average tempature, average precipitation, and modeled soil moisture for 2018.
A series of geospatial maps are included for each of the target species; the current map is followed by the previous 4 years.
For some species, the geospatial maps represent 2018 distributions used to infer risk in the coming 2019 growing season. Data is included for bertha armyworm, cabbage seedpod weevil, pea leaf weevil, wheat stem sawfly and diamondback moth.
For wheat midge and grasshoppers, the geospatial maps forecast or predict expected populations or risk for the 2019 growing season.

The historical Risk and Forecast Maps (2015-2019) are available for review.

These maps help the agricultural industry prepare to manage insect pests across the prairies and helps growers make crop choices and anticipate scouting priorities within their growing region. From May to July, the Weekly Updates will provide in-season updates, predictive model outputs plus scouting tips and links to relevant information.

Thank you to the many people who monitor each growing season!

Insect of the Week – Natural Enemies of the wheat stem sawfly

This week’s Insects of the Week are the natural enemies (@FieldHeroes) of the wheat stem sawfly, namely Bracon cephi (Gahan) and B. lissogaster (Hymenoptera: Braconidae).

Nine species of parasitic wasps are known to attack wheat stem sawfly but Bracon cephi and B. lissogaster are the main species that help regulate this pest in North America. These closely related wasp species are described as idiobiont ectoparasitoids meaning the parasitoid larva, after hatching from an egg laid on the surface of the sawfly larva, feeds on the exterior of the host. Normally, both Bracon species will complete their development (i.e., pupates) inside the wheat stem within the integument of the sawfly larva or just beside the consumed host. There are two generations of B. cephi and B. lissogaster per year. The first generation normally completes its lifecycle then escapes from the wheat stem to locate a new sawfly larva to parasitize. The second generation of these wasps will overwinter within the wheat stem.

These wasps are 2-15 mm long and are usually brown in colour. They have a narrow waist connecting the abdomen to the thorax and the combined length of head plus thorax is equal to the length of the abdomen. These parastiod wasps have long antennae and two pairs of transparent wings. Females have a noticeable ovipositor protruding from the end of the abdomen.

For more information about the natural enemies of the wheat stem sawfly, check out our Insect of the Week page!

Insect of the Week – Wheat stem sawfly (Cephus cinctus, Hymenoptera: Cephidae)

This week’s Insect of the Week is the wheat stem sawfly (Cephus cinctus). Adults are 8-13mm long and have a shiny, black, wasp-like body and yellow legs. When at rest on plant stems, they point their heads downwards.

Mature larvae overwinter in the base of stems in infested fields. In June, females emerge and fly to nearby wheat crops, where they can lay up to 50 eggs each on stems.

The wheat stem sawfly feeds primarily on spring and durum wheat, though winter wheat, rye, grain corn, barley, and some native grasses can support sawfly development. It cannot develop on oats.

Larvae feed on the pith of host plants stems which can cause a reduction in crop yield and quality. When plants mature, larvae move to the bottom of the stem to overwinter.

For more information about the wheat stem sawfly, head over to our Insect of the Week page!

Wheat stem sawfly – adult
(Alberta Agriculture and Rural Development)

Wheat stem sawfly – egg, larva, adult, damage
(Art Cushman, USDA Systematics Entomology Laboratory, Bugwood.org)

Weekly Update – Wheat surveying (post-harvest)

Wheat surveying – As wheat is harvested, monitoring can begin for two wheat pests including wheat midge and wheat stem sawfly. As soon as the combine passes through, in-field monitoring can commence with:
● Soil core sampling is used to assess the densities of wheat midge cocoons set to overwinter, PLUS
● The number of cut stems can be counted to determine the density of wheat stem sawfly.

By January, forecast and risk maps summarizing surveying efforts for the above pests will be available (e.g., check the Risk Map Page).

More information about these pests can be found by accessing the pages from the new “Field Crop and Forage Pests and their Natural Enemies in Western Canada: Identification and Field Guide”. View ONLY the Wheat midge pages or ONLY the Wheat stem sawfly pages. Remember the entire guide is available as a free downloadable document as both an English-enhanced or French-enhanced version.

Information related to wheat midge biology and monitoring can be accessed by linking to your provincial fact sheet (Saskatchewan Agriculture or Alberta Agriculture & Forestry) or the PPMN protocol.

Information related to wheat stem sawfly is posted by Alberta Agriculture & Forestry, Saskatchewan Agriculture, Manitoba Agriculture, or the PPMN.

Weekly Update – Wheat surveying (post-harvest)

By January, forecast and risk maps summarizing surveying efforts for the above pests will be available (e.g., check the Risk Map Page).

2017 Risk and Forecast Maps for the Prairies

The 2017 Prairie-Wide Risk and Forecast Maps can be viewed and downloaded here. Maps are generated for bertha armyworm, grasshoppers, wheat midge, cabbage seedpod weevil, pea leaf weevil, wheat stem sawfly, diamondback moth as well as average temperature, average precipitation, and modeled soil moisture for the Canadian prairies.

Thank you to the many people who monitor each growing season! An astonishing 6414 survey stops were involved in the insect monitoring performed across the Canadian prairies in 2016!

Alberta 2017 Forecast and 2016 Risk Maps plus updates to Alberta Agriculture and Forestry web pages

Alberta has posted their forecast and survey maps for several insect pest species occurring in field crops. Visit their home page to view all the Alberta maps.

The following list and hyperlinks were provided by Shelley Barkley via the Alberta Insect Pest Monitoring Network.

Scott Meers, entomologist with Alberta Agriculture and Forestry, was interviewed and spoke about Alberta insect forecasts for 2017. That series of five interviews can be access with the following hyperlinks:

Additionally, Alberta Agriculture and Forestry has updated their webpages with the following:

They have created a graphic that illustrates the “range expansion” of 2 evil weevils in Alberta: pea leaf and cabbage seedpod.
Similar graphics have been added to their bertha armyworm page. Check out the past “six years of bertha armyworm moth” in Alberta which can be accessed via an hyperlink positioned on their bertha armyworm web page.
Their grasshopper page has been updated too – check out the “historic grasshopper maps” for Alberta via a hyperlink located on their grasshopper web page.
The past “eight years of sawfly” in Alberta can be accessed via a hyperlink located on their wheat stem sawfly web page.
Remember, if you have access to a large format printer, a poster of the 6 Alberta insect forecast maps is available to print.

2016 Risk and Forecast Maps for the Prairies

The most recent insect pest maps of the 2016 forecast maps can be viewed and downloaded here.

Ongoing Monitoring Efforts for 2015

In 2014, the PPMN compiled data for the following sites highlighted in the map below. The monitoring data collected from these sites forms invaluable sources of information both now and into the future.

Agricultural people from federal, provincial, regional and industry sectors all contribute to this tremendous effort! Monitoring at sites like these below provides crucial information on insect pest risk before and during the growing season. Some sites are visited annually while others are checked weekly and all that data enables the synthesis and generation of risk and forecast maps like those posted here.

THANK YOU to all who contribute!

Please contact Dr. Owen Olfert at AAFC-Saskatoon for more information about this map.