Research detective work into understanding the population dynamics of the wheat stem sawfly is yielding important clues to help control this insect, which has risen to become the most damaging and costly pest of wheat in Western Canada.

"Learning more about the sawfly, particularly its behavior and population dynamics, will help farmers forecast their risk and apply more sophisticated control strategies," says Dr. Hector Carcamo, who is leading the entomology component of a new multi-faceted sawfly project by Agriculture and Agri-Food Canada (AAFC.) "There's a lot we've learned about the sawfly already thanks to our many predecessors at Lethbridge and Swift Current, who devoted most of their careers back in the 1950's to the study of this insect; we hope to expand on their contributions over the next several years."

The sawfly project is supported in part by wheat producers through the Wheat Check-off Fund, administered by Western Grains Research Foundation. While its main focus is developing 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, says Carcamo.

"The most recent cycle of sawfly resurgence began several years ago and has resulted in major losses for producers, who have had limited control options. We believe integrated strategies are the best way to combat this and achieve effective pest management over the long-term. Integrated strategies ensure producers take advantage of all available tools and management options and use the best knowledge to apply them. They also help prevent reliance on one or two options, which can leave less protection and put more pressure on pest populations to build resistance."

Past years of research have generated new knowledge of the sawfly that can help improve both risk assessment and control, he says. For example, researchers have learned the sawfly doesn't do well under wet conditions. "This supports the idea that the past two years of drought in large areas of the Prairies may have contributed to recent infestations. Another contributing factor is larger, re-cropped fields that provide a greater opportunity for the insect."

Another important finding is that previous year's sawfly numbers are a good indication of the next year's risk, he says. "Sawflies have high reproductive potential - on average, they lay 40-50 eggs per female. A field with as low as 20 percent sawfly infestation this year can be enough to result in an infestation of up to 80 percent in a nearby susceptible field the next year."

Timing is also important, says Carcamo. "We've learned the sawfly has a very narrow window of time for flight. Their activity is temperature dependent, but they most often emerge and fly during the last week of June and the first week of July. The males come out first and wait for the females to come out, to mate."

Among other findings, researchers have learned the sawfly has a poor ability to discriminate which host would be more suitable for its development. They have also identified a trend that thicker wheat stems - a trait independent of stem solidness - tend to be associated with the development of larger larvae and more fertile females. "Both types of information offer opportunities for developing control methods," he says.

In the new project, a key aspect researchers will look at is the effects of specific cultivars on sawfly population dynamics, in relation to weather and overwintering survival. "We have established that solid stem varieties produce smaller larvae and fewer females. We also know that there is less cutting in solid stems, but we haven't examined how this relates to the overwintering survival of the sawflies. For example, if a larva is not able to mine its way all the way to the crown area where they overwinter, they will be exposed to much colder temperatures, which could reduce their survival chances."

Another question researchers hope to answer is how far the sawfly moves, says Carcamo. "This will help us get a better idea of the potential for trap cropping, while supporting other risk assessment and control strategies."