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An important new research paper has recently been published on leafy spurge biological control. The Biological Control of Leafy Spurge is a well written, comprehensive overview of leafy spurge biological control—and a confirmation that the YRLSP is on the right track with its biocontrol release project. Click on the title in the previous sentence, or visit our Resources pages, where you will find links to this paper as well as other valuable sources of information on leafy spurge and its management.
Although conventional herbicide treatment of upland leafy spurge infestations has been the norm in the Yampa River Basin, the use of biological control agents also dates back to at least 1989. Unfortunately, in the early years recordkeeping was sometimes incomplete, and (with the exception of Tepee Draw) virtually no follow-up monitoring was ever conducted. In the absence of such data, the relative success or failure of these “legacy” biological control releases remained unsubstantiated.
Leafy spurge biological control involves the introduction of one or more different insect species that have co-evolved with leafy spurge in its original old-world habitats. Unlike most herbicides, biological control is safe to use in riparian habitats, does not negatively impact desirable species, and has the potential to be self-sustaining. The most commonly released leafy spurge biological control agents in the Yampa River Basin have been multiple species of flea beetles in the genus Aphthona, as well as a stem-boring beetle (Oberea erythrocephala). The caterpillars of another introduced leafy spurge biocontrol species—the leafy spurge hawk moth (Hyles euphorbiae)—are frequently found on local infestations, although there is no record of a local release of that species.
The goal of biological control is control of the target species, rather than eradication, and the impact of biological control insects on leafy spurge can be quite different from conventional herbicide use. While herbicide applications may quickly provide obvious mortality of the plant's foliage, biological control acts more subtly to reduce leafy spurge's overall viability. Tall, dense, vigorously flowering stands will typically be reduced to patchier, sparsely flowering stands after the introduction of biological control. The result is reduced seed production—an important step towards reducing the waterborne seed load in the Yampa River and its associated irrigation delivery systems.
It is also possible to integrate the use of biological control with conventional herbicide applications. For more information on an integrated leafy spurge strategy, visit our Integrated Management page and consult with your county weed manager.
Leafy spurge biocontrol agents photographed locally.
Left top and bottom: Leafy Spurge Flea Beetles (black and brown species)
Right top: Leafy Spurge Hawk Moth Caterpillar
Right bottom: Leafy Spurge Stem-Boring Beetle
Biological Control Monitoring
The effectiveness of leafy spurge biological control in the Yampa River Basin cannot be quantified without a long-term monitoring program. The YRLSP’s efforts towards establishing a biological control monitoring program began in 2018, with the research and compilation of all available records for "legacy" (prior to 2018) leafy spurge biological control releases in Moffat and Routt counties. The location and year of release for over 40 legacy sites were identified. For most of these release sites we also have additional information regarding the type and quantity of insects that were released.
Legacy leafy spurge biological control releases date back three decades.
Beginning in the summer of 2019, volunteer Tamara Naumann, with help from individuals associated with the local Colorado Master Gardner program, and local, county, state and federal land agencies, began revisiting these legacy biocontrol release sites. Using a sweep-net protocol, the current presence or absence of biocontrol insects at each legacy site was established, and the current condition of the leafy spurge infestation was assessed. Other habitat variables (e.g., geomorphic location, aspect, soil type and dominant vegetation) were also inventoried. Each site was then evaluated for its appropriateness for continued biological control monitoring in the future.
The results from Tamara's monitoring confirmed that past releases of biological control species in the Yampa Basin have been far more persistent than was conventionally thought. At least one biocontrol species has been found at virtually every visited legacy release site where leafy spurge is still present. Aphthona, Oberea and Hyles have also been observed in many additional locations, often many miles from any documented previous release site. For example, leafy spurge biological control species were found in the Axial Basin, the Little Yampa Canyon, remote patches of leafy spurge in upland habitats northeast of Maybell, and along the Yampa River in Dinosaur National Monument—all areas where no legacy releases had ever been documented. (Since the commencement of the YRLSP biological control project in 2019, leafy spurge biocontrol insects have been released in all of these areas).
The widespread presence of leafy spurge biological control insects throughout the Yampa River Basin, even in relatively low numbers, confirms their viability in these habitats, and suggests the possibility that over the last three decades biological control insects have already been at work slowing the growth of leafy spurge infestations.
Sweeping for leafy spurge biocontrol insects along the Yampa River.
Biological Control Releases
YRLSP's monitoring data is already contributing to a better understanding of the resiliency of the various biological control species in association with differing environmental conditions. This information is invaluable for establishing enhanced biocontrol populations through additional releases in the future.
To this end, in cooperation with our agency partners and multiple private- landowning stakeholders, in 2019 the YRLSP began an accelerated leafy spurge biological control release program. The goal is to distribute Aphthona (flea beetles) and Oberea (stem-boring beetles) in appropriate locations throughout the full extent of the riparian habitats of the Yampa Basin, from Hayden to Dinosaur National Monument. Each new YRLSP release site will be subject to continued biological control monitoring in the future.
Currently leafy spurge biological control insects are available to us (in seasonally variable quantities) from collections made by the Colorado Department of Agriculture (CDA) at various Colorado Front Range locations, from a commercial vendor collecting in Montana, and more recently we have initiated what we expect to become annual collection trips to locations in Idaho. However, ultimately the YRLSP hopes to also establish a number of viable local nursery sites for its own Yampa-Basin-sourced beetle collection and redistribution.
As the YRLSP has become proficient at collecting leafy spurge biological control insects for redistribution in the Yampa Basin, the potential for increasing our annual release numbers has grown. Early on, a tentative goal was set to release at least 100,000 biocontrol insects in the Yampa Basin over the first five years of the biocontrol program. We are happy to report that we have now exceeded this goal (see the downloadable table below), and we anticipate many more successful releases yet to come in the future.
Overview of the first five years of YRLSP biological control releases.
These totals include releases made by our county and federal partners.
What follows is an overview of the biological control releases made by the YRLSP and its partners in the Yampa Basin.
In the first year of the YRLSP biological control release program, approximately 7,300 flea beetles collected by the CDA on the Front Range (and donated to the YRLSP) were released on or in the vicinity of the Yampa River State Wildlife Area (YRSWA).
In June 2020, four YRLSP volunteers upped the ante by traveling to the Front Range to aid the CDA in their annual collection of leafy spurge biological control beetles. Under the tutelage of the CDA's John Kaltenbach, on the first day approximately 27,000 flea beetles were collected from the former Lowry Bombing and Gunnery Range east of Denver. Day two was then spent at the CDA facility in Broomfield, sorting the flea beetles from stray plant parts and the rest of the insect "bi-catch," before packaging them into 1000-insect lots for distribution by the CDA across Colorado. In return for our contributions, the YRLSP's share of the take was thirteen 1000-insect lots of Aphthona, and one lot of Oberea (Oberea is typically released in lots of only 100 insects).
Upon our return to the Yampa Yalley, two additional days were spent releasing the biological control insects at thirteen separate locations in Routt and Moffat counties. In June, Routt County Weed Program released 500 Aphthona northwest of Hayden. Then, in July 2020, YRLSP volunteers also helped release an additional 10,000 flea beetles on the Yampa River State Wildlife Area, purchased by the YRSWA from a vendor in Montana.
This brought the total for just the 2020 biological control releases alone in the Yampa Valley to approximately 23,600 insects—roughly a third as many again as recorded during the entire "legacy release" period of 1989–2017!
The YRLSP was looking forward to another successful volunteer collection trip to the former Lowry Bombing and Gunnery Range in 2021, but (despite the extreme drought conditions prevailing on the Western Slope) continuously cool, wet spring conditions on the Front Range resulted in poor collection numbers during test runs by CDA crews. Ultimately it became clear that a collection trip to the Front Range by YRLSP volunteers would have produced only limited returns.
Nevertheless, John Kaltenbach of the CDA was able to supply us with 3,000 Aphthona and 250 Oberea, while Tyler Jacox of Colorado Parks and Wildlife (CPW) was able to acquire an additional 6000 Aphthona and 200 Oberea from the Montana vendor. All of these insects were released at new locations in the Yampa River State Wildlife Area and Moffat County. The Routt County Weed
Program also released another 1000 Aphthona northwest of Hayden.
Aphthona biological control beetles dispersing from the lid of their container during a 2022 release in the Little Yampa Canyon.
The YRLSP again traveled to the former Lowry Bombing and Gunnery Range in June of 2022, for another successful volunteer collection trip under the auspices of the Colorado Department of Agriculture. This time we brought home approximately 12,000 Aphthona and 200 Oberea, which were quickly released at sites in Moffat County. Another 2000 Aphthona from the Lowry collection were later released by John Kaltenbach in the Yampa River State Wildlife Area, during our two-day Youth Outreach event.
Tyler Jacox of the CPW was again able to procure an additional 6000 Aphthona and 300 Oberea from the Montana vendor, all of which were also released in the Yampa River State Wildlife Area. A last-minute, surprise gift of an additional 4000 Aphthona were also added to the new releases on the YRSWA. (Originally intended for release in the White River basin, these were donated to the YRLSP by Deirdre Macnab of the White River Alliance, after they were mistakenly delivered to an address in Steamboat. With the clock ticking, and no one with the White River Alliance readily available to pick them up, Deirdre turned to the YRLSP for help rescuing the beetles.)
The YRLSP also purchased an additional 6000 Aphthona and 200 Oberea from our Montana source, which were released at five sites in Moffat County. Finally, the Routt County Weed Program also released an additional 1000 Aphthona on private lands south of the YRSWA.
Overall, in 2022 a total of 18,400 biological control insects were released in Moffat County, and another 13,300 in Routt County, for a combined total of approximately 31,700 biocontrol beetles for the season.
Containers of Aphthona and Oberea collected in Idaho await transportation back to the Yampa Basin.
The YRLSP expanded its biocontrol horizons in 2023 by traveling to Ashton, Idaho, to meet with Kim Ragotzkie, a contractor with the BLM. Kim and the YRLSP crew collected about 17,000 Aphthona and 1,000 Oberea in 3 to 4 hours on their first morning, and then spent another day and a half sorting the beetles from the by-catch (non-target insects and vegetation debris). After returning to Colorado, the majority of these beetles were immediately released on the YRSWA the next day. Shane Talvacchio of the CPW had also purchased 6000 Aphthona and 300 Oberea from Montana, and coincidentally these were delivered to Shane just the day before, so by the end of the afternoon Shane and the YRLSP crew had collectively released 23,400 beetles on four sites in the YRSWA. The remainder of the Idaho catch, another 1,000 Aphthona and 100 Oberea, were released at Deerlodge Park in Dinosaur National Monument.
The CDA also supplied more beetles to the Yampa Basin this year than in any past year. Dinosaur National Monument received 12,000 Aphthona and 100 Oberea from the CDA in early July, for release in the monument’s Yampa Canyon. In late June, the Routt County Weed Program released 3,000 Aphthona from the CDA. The next day, the participants of the YRLSP's Show Me Float released another 5000 Aphthona and 170 Oberea on private lands just upstream from the Yampa Valley Golf Course. John Kaltenbach of the CDA then supplied an additional 9,000 Aphthona and 100 Oberea, which he released on the YRSWA during the YRLSP's Youth Outreach events in mid-July. The total for the beetles received from CDA in 2023 for release in the Yampa Basin came to 29,000 Aphthona and 370 Oberea.
Thus, the total leafy spurge biological control insect releases made by the YRLSP and its partners came to a whopping 53,670 in 2023 (see table below).
Biological Control Gallery
Terry, John and Ben, ready to start collecting leafy spurge biological control species at the former Lowry Bombing and Gunnery Range.
Ben sweeping leafy spurge for biological control species at the former Lowry Bombing and Gunnery Range.
A leafy spurge longhorn stem-boring beetle, Oberea erythrocephala.
Terry, John and Ben, ready to start collecting leafy spurge biological control species at the former Lowry Bombing and Gunnery Range.