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An early warning system for pea leaf weevil

Three years of producer-funded research enabled the development of a semiochemical-baited trap to monitor pea leaf weevil in the prairie provinces.

Pea leaf weevil is a tiny insect that punches far above its weight in terms of potential impact on crop yield. The size of a grain of rice, this non-native invasive insect has emerged in recent years as a threat to Alberta’s most-planted pulse crop.

Complicating growers’ pea leaf weevil defense is the fact that this insect appears intermittently. Some years it’s a significant problem, while in others it’s just a minor inconvenience.

What if pea growers had a way to determine whether next year’s pea leaf weevil activity was likely to be problematic?

University of Alberta entomologist Maya Evenden spent three years working on just such a solution. With support from Alberta Pulse Growers, via the Alberta Crop Industry Development Fund, Evenden has developed the tools for a pea leaf weevil monitoring system.

Two naturally occurring chemicals as bait

“There are two times in the life cycle of pea leaf weevil where you can monitor adult activity,” Evenden said. “You can do it in the spring when adult weevils come into the field and in the fall when the next generation of adults leave the field in search of overwintering locations. You can use traps in the fall to check them when they go to overwinter. That would tell you whether or not you needed to use an insecticide seed treatment the following spring.”

As Evenden explains, her pea leaf weevil monitoring traps required some type of bait to attract weevils. She used two different types of semiochemicals, or information-bearing chemicals: an aggregation pheromones and volatile chemicals emitted by pea plants.

Over three years of field studies, Evenden used a variety of trap configurations, and various combinations and doses of aggregation pheromone and/or volatile chemicals as bait.  Many field trapping studies were conducted in commercial field pea crops during three field seasons to optimize the best bait and trap type to attract and retain weevils.

In addition, Evenden’s team conducted a painstaking mark-recapture experiment over two years that involved the collection of approximately 20,000 weevils from pea fields. Of these, 10,000 were marked with a spot of nail polish on the thorax. The marked weevils were released at eight different distances from the traps to test the traps’ effective radius. As very few marked weevils were trapped in this experiment, more work is needed to establish how many traps might be needed, given the size of a field, for monitoring of pea leaf weevil populations.

After three years of field work led by Evenden, there is now a practical tool for monitoring pea leaf weevil. Evenden’s work with this insect will continue. Building on knowledge gained in the monitoring project, she’s now working to determine the extent of pea leaf weevil in the province.

“We’ve learned a lot about the chemical ecology of weevils and are now tracking it all over Alberta to get a field-scale reading of where pea leaf weevil is,” Evenden said.

Project at a glance

Project title:                Development of semiochemical-based monitoring of the pea leaf weevil

Project lead:                Maya Evenden, University of Alberta

Total value of project: $135,993

Start date:                   April 1, 2013

Completion date:        October 31, 2016