JACKSON, Wyo. — Teton County Weed and Pest (TCWP) is currently using biological control agents to reduce the competitiveness of seven invasive species, with newly approved host-specific agents on the horizon.
TCWP implements classical biological control, which TCWP Entomologist Mikenna Smith defines as the practice of importing and releasing host-specific natural enemies, usually insects, to control an invasive, non-native weed species. Smith says finding a host-specific natural enemy, also known as a biocontrol agent, is one of the most important parts of this; this means that if the invasive weed species were to die, the insects that were brought in to control them would die as well.
However, since the biocontrol agents are not sourced locally, each species needs to be approved for release in the U.S. through a rigorous process that can take more than a decade. This April, Smith visited the Centre for Agriculture and Biosciences International (CABI) in Switzerland, where researchers study collected organisms that are potential host-specific agents over the course of 10+ years in collaboration with TCWP.
After the research is completed, Smith says the host-specific species then needs approval from the U.S. Department of Agriculture (USDA) and must go through quarantine prior to local introduction. Because of this extensive research and strict approval process, Smith says the risk that using biocontrol agents will harm native wildlife in Wyoming is very low. A new species won’t get approved if the USDA committee thinks any of the research suggests there is a risk.
In Teton County there are currently seven plants with biocontrol agents on them, and some plants have multiple agents.
“The more biocontrol agents you can put out for a single plant, the more natural enemies that plant has,” Smith tells Buckrail. “The more biocontrol agents, the better.”
Smith points to the Spotted Knapweed, which has a Spotted Knapweed Flower Weevil reducing the seed output and a Knapweed Root Weevil chewing at the roots, as an example where biocontrol agents are working together to attack different parts of the plant.
TCWP categorizes weeds according to a priority scale one through four. Priority One means invasive plants need to be eradicated as soon as possible before they establish in the local landscape, which Smith says is not a good fit for biocontrol.
Priority Four species, however, are the optimal candidates for biocontrol treatment. According to Smith, Priority Four plants like Musk Thistle and Spotted Knapweed are very widespread and will never be eradicated; because of this, the goal for these invasive species is to reduce their competitiveness by reducing their seed output, their ability to conduct photosynthesis and their ability to grow roots, among other things.
“Biological control makes sense for the Priority Four species,” Smith says. “The goal for biocontrol is often not to eradicate, that occurs in rarer cases. The biocontrol introduces a competitor. Invasive species take over a new place because they have no natural enemy controlling their local population.”
Unlike herbicide spraying, biocontrol can take years to see results. That’s one of the reasons Smith is pushing for more post-release monitoring locally and statewide, especially after speaking with CABI researchers and hearing how helpful this information would be for them as well. Collecting more data on how introduced insect agents are doing would allow TCWP, CABI and the Biotechnology Biocontrol Agency (BBCA), a collaborator with CABI based out of Italy, to better understand the effectiveness of the chosen agents.
Thus far, Smith reports the best performing biocontrol agents have been on Spotted Knapweed, Dalmatian Toadflax and Musk Thistle. Smith notes one instance where TCWP had a spray crew scheduled to do treatment on Dalmatian Toadflax but the biocontrol agents had done such a good job that the spray was canceled.
While some of the biocontrol agents have been out in the Jackson Hole landscape since the 1990s, a new agent has recently been approved for oxeye daisy: a moth that in its larvae stage mines the root of the plant.
“A root miner is the most effective biocontrol agent,” Smith says. “Which is really exciting because oxeye daisy is everywhere here.”
Smith says she’s been doing pre-release baseline data collection in anticipation of getting the new agent, which she expects will happen in the next couple of years.
Additionally, Smith shared that a biocontrol agent for Houndstongue is getting close to completing the permitting process as well, and says there are more in the pipeline at all times. Notably, there is also preliminary research being conducted on cheatgrass biocontrol through BBCA. While cheatgrass biocontrol is in its infancy of the research stage, Smith says it has the potential to be very impactful to western states that are suffering from invasive grasses like Wyoming.
In Teton County, Smith confirms cheatgrass is considered a Priority Four invasive species that hasn’t gotten out of control yet, unlike in other parts of the state.
“I don’t want to say [biocontrol] would be the end-all-be-all fix, but integrated pest management does focus on using as many tools in the toolbox as possible and biocontrol is absolutely one of those aspects, along with chemical, mechanical and cultural methods,” Smith says.
Hikers, bikers, riders, campers and all other recreationists are encouraged to help stop the spread of invasive species by cleaning outdoor belongings and gear before and after use, staying on designated trails, observing “buy it where you burn it” when using firewood, feeding horses weed-free certified hay and removing mud and plants from all pet fur.
