Solid-stemmed wheat varieties can substantially reduce the over-wintering survival of the wheat stem sawfly, which has become the most damaging insect of wheat in Western Canada.

"Research this past winter showed that solid-stemmed wheat varieties hamper the over-wintering survival of sawfly larvae," says Dr. Hector Carcamo, who is leading the entomology component of an ongoing, multi-faceted sawfly project by Agriculture and Agri-Food Canada (AAFC). "Previous research had demonstrated that varieties with greater stem solidness result in smaller larvae and fewer females, but we had not examined the specific impact on over-wintering survival."

The AAFC sawfly project is supported in part by grain producers through Western Grains Research Foundation (WGRF). While the project's main component is breeding wheat varieties with a greater degree of stem-solidness, which is a source of sawfly resistance, the ultimate goal is to use these varieties as part of integrated control strategies that take advantage of better overall sawfly knowledge. Carcamo's research has focused specifically on understanding sawfly behaviour and population dynamics.

"In the larval over-wintering study, we are finding that larvae that develop in hollow-stemmed varieties have greater cold-hardiness than those that develop in wheat with greater stem solidness," says Carcamo. "The over-wintering survival at -20 C over 20 days in a laboratory study was 25 percent lower in the solid-stemmed wheat."

The female sawfly inserts its eggs into the hollow stem of the wheat plant and the larvae develop inside the stem and damage it, explains Carcamo. Researchers have established that wheat with greater stem solidness reduces the sawfly population in several ways - eggs are crushed during egg laying, larvae have greater difficulty tunneling within solid stems and become malnourished, and females have reduced fertility the following spring. "These latest findings further show that reduced sawfly health contributes to lower over-wintering survival," he adds.

The sawfly risk forecast for this year is similar to recent years, says Carcamo, with large areas of the western Prairies experiencing a moderate to severe infestation risk. "A good way to predict risk for the following year is to look at damage last year. A field with as low as 20 percent sawfly infestation can result in 80 percent infestation the following year because of the reproductive potential of female sawfly."

Sawfly infestation and damage to wheat crops has increased dramatically over the past five years, particularly throughout the Palliser Triangle of southern Alberta and southwestern Saskatchewan. This year, says Carcamo, researchers are seeing a broader risk area, including areas further north such as Lloydminster and Vermillion.

For producers, aside from shifting wheat rotations, the main control option is growing varieties with greater stem solidness. Two key varieties, AC Eatonia and the newer AC Abbey, are available to producers. Lillian, a new line featuring improved yield and protein content is expected to be available in 2005.

"Unfortunately, we've found that some farmers in areas with a moderate to severe risk of sawfly aren't planting the current varieties that have greater stem solidness because of the yield penalty they carry," says Carcamo. "But those farmers should keep in mind that by growing a hollow-stemmed variety they run the risk of even lower yields because of sawfly damage."

Lillian, developed by AAFC's Semiarid Prairie Agricultural Research Centre in Swift Current, will offer producers the best of both worlds, says Carcamo.

"Lillian has the stem-solidness needed to limit sawfly survival and damage," he explains. "It also has yields and protein levels that rival traditional hollow-stemmed varieties, even when those hollow varieties are grown under no sawfly pressure. We expect there will be tremendous demand for this variety next summer in areas under sawfly risk."

The producer-funded Wheat Check-off Fund, administered by WGRF, allocates over $4 million annually to wheat breeding programs in Western Canada, including breeding efforts for sawfly resistant varieties. The broader AAFC sawfly research project is supported primarily by government funds matched to these farmer dollars through AAFC's Matching Investment Initiative and royalties earned on WGRF-funded cultivars.