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Inside the world of the wheat stem sawfly

The sawfly has risen to become the most damaging insect of wheat in Western Canada. New research that probes its behaviour will help provide a defense, says Dr. Hector Carcamo.

The wheat stem sawfly has cut a wide swath out of farmer profits in recent years. Now, a team of western Canadian researchers plans to turn the tables on the insect, with a new, multi-faceted project.

A key member of the research team is Dr. Hector Carcamo, an entomologist at Agriculture and Agri-Food Canadada's (AAFC) Lethbridge Research Centre, who is delving into the world of the sawfly to learn about the insect's behavior patterns. Here, he provides some perspective on what he and other reseachers are learning and how this can help farmers defend against the sawfly, which has risen to become the most damaging insect pest of wheat in Western Canada.

Weather key to population changes

Understanding sawfly behavior and population dynamics is also very important to help farmers forecast their risk and apply the right integrated management practices to control those populations. There's a lot we've learned about the sawfly, and we plan to expand on this under the new project.

For example, we know the sawlfy doesn't do well under wet conditions, so the past couple years of drought may have played a role in the high numbers we've seen. But it's important to remember that we have a history of sawfly infestation cycles. At times the population gets suppressed by weather conditions or natural enemies. In the current wave, one contributing factor is larger, re-cropped fields that provide a greater opportunity for the insect.

Narrow window of flight time

We also know previous year's sawfly numbers are a good indication of the next year's risk. Because an infested wheat cultivar can contain 40-50 sawfly eggs, 20 percent cutting in one year can rapidly expand to 70-80 percent cutting the following year.

Timing is also important. 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, then they mate.

Wheat type, mining activity influence survival

The sawfly has poor ability to discriminate which host would be more suitable for their development. There is also a clear trend of larger larvae and greater fecundity of females that come out of thicker stems. Both types of information offer opportunities for developing control methods.

In the new project, a key aspect we'll be looking 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 they interact with the overwintering survival of the sawflies. For example, if a larvae 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 we hope to answer is how far the sawfly moves. This has implications for the potential of trap cropping, among other risk assessment and control components.

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