Bio-control agents unleashed: Southern Alberta leading the way for targeted invasive weed-control measures

By Tim Kalinowski


Invasive plant species often come to Canada with no natural predators or grazers, allowing them to out-compete most natives species and take control of vast areas of the rangeland and parkland landscape.

Spraying can help, but is not a long term solution to the problem. Sprays also cannot be used in landscapes where native species are vulnerable or when there are water bodies nearby. So what’s the solution? Robert Bourchier, an entomologist at the Agriculture and Agri-Food Canada research station in Lethbridge, might have part of that answer.

For the past 20 years Bourchier has been one of the lead researchers on AAFC’s operational bio-control program, which seeks to import beneficial insects from invasive species’ native homelands to Canada. The testing and screening facility for these potential bio-controls is housed at the Lethbridge Research Station.

“We have had an operational bio-control program in southern Alberta since 2001, with collaboration initially between six municipal districts,” explains Bourchier. “The targets for that have been leafy spurge, knapweed, toad flax, and hound’s tongue. We have been releasing insects against those four targets on an ongoing basis since 2001.

“There is basically a pipeline of insects that go through a series of stages of identification and screening to ensure they are safe,” he adds, “and then analyzed to see what sort of impacts they can have before they go to the operational level where they are being released and redistributed to have impact on the weeds.”

“Safe” in this case means targeted. Bourchier says each insect eventually released as a bio-control agent against invasive species like knapweed, for instance, only have a taste for the plant they are being released to go after, with no collateral damage to other native plant species at home on the landscape.

“All the weeds we are targeting are introduced, they come from Europe, Japan or Asia, so when they come here they have no natural predators that feed on them,” Bourchier says. “What we are doing is identifying what those natural herbivores are in their native range that are very specific to the target weed. The ones that are eventually released will only eat the target weed.”

Bourchier says unlike chemical controls, releasing bio-control agents may take up to 10 years to eliminate, or greatly reduce, the number of invasive weeds in a particular area. That’s why they are used more for invasives on rangelands where the economics of spraying does not make sense for a producer, and is often too difficult to carry out.

“It may or may not work everywhere,” Bourchier says. “It’s important we realize that. For example, with leafy spurge we have two different flea beetles that are quite effective at controlling leafy spurge on open rangeland. By that, you release it, over the life of the program, you can expect visible damage in the first couple of years around where you have released it, and then the beetles move out from that spot and you get a halo of dead spurge that will gradually expand. But you are dealing with a weed that often has a 100 year head start.”

Knapweed is another weed where bio-controls have proven success but those controls have only been active for a relatively short period of time, he says.

“The problem with knapweed, like many of these weeds, is they produce an incredible amount of seed. What we are working at with the knapweed program is to get these insects out there that will reduce the seed production in terms of the seedhead insects, and then we will kill the plants in terms of the root feeders. But you are working against that long-term seedbank, and you have to exhaust it. You can kill a lot of seed right now, but you have to wait until the other seed germinates. So it is a long-term process.”

Perhaps with the exception of hound’s tongue weevils, Bourchier says rarely does a bio-control agent come out of the gate with the ability to have a major impact in its first few years, and it takes several generations of the introduced insect specialists to acclimatize and establish themselves in the landscape. That’s why it is important to set up nesting programs with regional partners, he says.

“One of the things with this operational program when we first started the goal was to get a nest site in each of the participating municipal districts where they could recollect the beetles and redistribute them. That has value because the beetles are locally adapted to the conditions where that MD might be. We hit that about 2006 where each of the initial MDs established those sites.

“What we have seen over the life of the program, for example, is we are getting faster impacts from the release of locally adapted leafy spurge beetles then we did when we imported them in from farther away— even when they come from just across the border in Montana, for instance.”

Bourchier says today’s bio-control researchers are more conscious than ever of the importance of the work they are doing, but also adhere to much stricter principles when deciding whether or not to allow an introduced species out of the lab onto the landscape.

“Recently there was a review of over 500 insect agents released around the world,” he explains. “In all of those situations there is very good (screening) track record. There were only two insects of the 500 which had fed unexpectedly on something that was not targeted. Those two were also legacy programs, releases which happened in the 1970s, and that type of insect wouldn’t be released today. So the safety profile is pretty enviable.”

Bourchier admits that values have also changed since the first bio-controls began to be released in the 1950s in terms of what compromises are acceptable to bring an invasive weed under control. He gives the example of nodding thistle as an early success story in Western Canada following the release of a bio-control agent, but also the trade-offs researchers and the agricultural industry as a whole were willing to make at the time.

“The big focus then was to ensure the insects wouldn’t attack a crop,” says Bourchier. “In the late 1960s (the nodding thistle weevil), it was known that species would also feed on native thistle if released, but at that time the trade-off was considered to be worth it. We didn’t care about native thistles. Now we have a much different value system in terms of threatened and endangered species, and those agents wouldn’t be considered as agents today.”

He does add, however, the success of the introduction of this weevil, even with all its downsides, is the reason we do not have a nodding thistle problem on the Prairies today.

“If you do find nodding thistle on disturbed land beside railways or wherever, we don’t do anything about it anymore because the weevil will find it and take it out after a few years. So it is a big success in controlling nodding thistle, but the flipside of that is that weevil will also attack some of the native thistles that are of concern in Waterton Park, for example. To people trying to protect those native thistles, it is a pest.”

Bourchier says if he has done his bio-control job correctly, those out enjoying a walk on the prairie in south western Alberta or in Waterton Lakes National Park will not even notice.

“When bio-control works, the weed is gone. You didn’t notice the agent at work,” he says.

Photos courtesy AAFC
Two Knapweed seedhead, weevils, Larinus minutus, feeding in a spotted knapweed seed head.
Knapweed root weevil, Cyphocleonus achates, searching for mates on the top of a spotted knapweed plant.
Black leaf spurge beetles, Aphthona lacertosa, swarming and feeding on leafy spurge.