YAMPA RIVER LEAFY SPURGE PROJECT
Highly Recommended!
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.
Introduction
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.
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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.
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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.
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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
Monitoring Biological Control
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.
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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).
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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.
In addition to collecting monitoring data on legacy sites, the YRLSP has also been establishing monitoring sites wherever we have made our own leafy spurge biocontrol releases (starting in 2019). As of the end of 2023, many of these release sites had been monitored only once, except those few where additional releases were made at the same location in subsequent years. The intention all along has been to establish a cycle of repeat monitoring at release sites, and in spring of 2024 a repeat monitoring schedule was drafted. The plan has now been updated through September 2024. To download a PDF version of the current monitoring rotation spreadsheet, click HERE.
Isolated monitoring/release sites will all be visited individually, while in areas of concentrated multiple releases the goal is to monitor a single location within the associated cluster of releases. Each of these sites, whether individual releases or defined "clusters" of releases, will be remonitored at least once every five years.
The newly funded Inundative Biological Control Strategy Project (IBCS), of which the YRLSP is a key partner, is anticipated to dramatically add to the existing number of release and monitoring sites in future years.
Releasing Biological Control
YRLSP's monitoring data has already contributed 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.
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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 downstream though 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 for purchase (in seasonally variable quantities) from collections made by the Colorado Department of Agriculture (CDA) at various Colorado Front Range locations, and from a commercial vendor collecting in Montana. More recently we have initiated annual collection trips to locations in Idaho, where we are able to collect our own leafy spurge biological control insects for release in the Yampa River basin. However, by continuing to bolster the Yampa basin biocontrol populations, we also hope to eventually establish a number of viable "nursery" sites for locally sourced beetle collection and redistribution.
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As the YRLSP has become more proficient at collecting our own leafy spurge biological control insects for redistribution in the Yampa Basin, the potential for increasing our annual release numbers has also grown dramatically. In 2019, 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 easily exceeded this goal in our fifth year.
To cap this success off, in 2024 we actually released well over 100,000 biocontrol insects in just one field season! We anticipate many more successful biological control release activities yet to come in the future.
If you are looking for the detailed narrative of the YRLSP's annual leafy spurge biological control release activities, click HERE.
Specific locations of individual releases (and the data collected at each site) are now displayed on our Interactive Map. The YRLSP biological control release and monitoring datasets can also be downloaded directly from our GIS Data page.
Aphthona biological control beetles dispersing from the lid of their container during a 2022 release in the Little Yampa Canyon.
Inundative Biological Control Strategy
In "classical" plant biological control programs, biocontrol insects are typically "seeded" into a target infestation by releasing a small quantity of insects, typically the minimum considered adequate for establishing a viable new population. The expectation is that, in time, the new population will naturally grow to numbers great enough to begin significantly impacting the target species. The classical methodology evolved under circumstances where biocontrol agents might be in limited supply (and expensive), so the emphasis is on distributing the available resource across the landscape as economically as possible.
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For Aphthona, the traditional number of insects considered viable for establishment is approximately 1,000. (The CDA provides Aphthona in 1,000-insect lots, while the Montana vendor provides them in 1,250-insect lots.) There is a good track record for establishing viable Aphthona populations using classical biological control methods in states such as Montana and Idaho, where dramatic reductions of leafy spurge populations have subsequently been documented.
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In the first few years of the YRLSP’s leafy spurge biological control program, we also followed the classical methodology, typically releasing one or two lots of Aphthona at each location (often in combination with a single lot of 100 Oberea), with a primary focus on distributing the available leafy spurge biological control agents as broadly as possible throughout the entire Yampa River basin.
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However, as larger numbers of biological control insects have become available for the YRLSP and its partners, the YRLSP has been able to shift to what we now call our “inundative biological control strategy.” Instead of releasing just a small quantity of biological control insects at one location within a larger leafy spurge infestation, we are now able to release greater numbers at a time, in multiple locations spread broadly across that infestation.
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Of course, there's a certain common sense about such a "more is better" approach. But there's also nothing novel about such a strategy in the insect world, where laying lots and lots of eggs guarantees that more progeny will survive to maintain, or even increase, the population of the next generation. As our access to biological control numbers has increased, the YRLSP has the option of focusing on boosting both local biocontrol numbers as well as extending their distribution in the region.
For the YRLSP’s purposes, the inundative strategy is particularly appropriate for establishing biological control populations in riparian habitats, where some periodic saturation of soils is a regular occurrence. Aphthona establishment in wetter environments is complicated by the insect’s lifecycle. Aphthona are particularly effective in leafy spurge control because the larval stage of the beetle’s lifecycle is spent below the soil surface, where they feed on the spurge roots. It's this damage done to the spurge root system that can seriously compromise the spurge's ability to grow, flower, and set seed. However, flooding during the early spring, before the Aphthona larvae pupate into the next generation of adults, can impact larval survival.
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Establishing larger populations more broadly across the matrix of local conditions found in the Yampa’s floodplains means that there will always be more surviving beetles close by and available to recolonize areas that might have been hit hard by spring flooding.
Collecting Biological Control
When the YRLSP began exploring the potential for doing leafy spurge biological control, it soon became evident that significantly boosting biological control beetle populations across the entire Yampa River basin was going to require releasing more insects than it was feasible to purchase. The alternative was to learn how to collect our own.
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In 2020, four YRLSP volunteers joined John Kaltenbach of the CDA on our first collecting trip, to the former Lowry Bombing and Gunnery Range east of Denver. Lowry has been the source for most of the Aphthona and Oberea the CDA has supplied the YRLSP over the years. The trip was a success, allowing us to bring home 13,000 Aphthona and 100 Oberea for release in Routt and Moffat counties—almost twice the total number of biocontrol insects we’d released the year before. We also learned first-hand the difficulties involved with collecting, sorting, and packaging biological control insects, which are unavoidably mixed with lots of unwanted insect species and plant debris when first netted in the field. It gave us an appreciation for the expertise, time and labor that went into creating those clean packages of biocontrol we’d received from the CDA in the past—with no plant debris and no non-biocontrol insects.
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Biocontrol insects are collected by sweeping the leafy spurge with an insect net. In addition to the target insects, the sweep net picks up lots of fine plant debris—so the first step is separating the insects from as much of the debris as possible. Getting the insects out of the mass of plant debris as quickly as possible significantly enhances their survival during the entire collection and redistribution process. Maximizing the initial sorting of insects from plant debris in the field can also save substantial time and labor later in the sorting process.
Over the past two decades, there have been many innovative, home-made “Aphthona accelerator” devices created by groups collecting leafy spurge biocontrol. Plans can be found on the Internet (though you won’t find a commercially made model for sale). But we quickly learned that there was still plenty of room for improvement. The YRLSP accelerator design has undergone many changes during our first few years of field testing. In fact, a major development was to recognize that the original “accelerator” design we started with was especially hard on Oberea, which are larger and more fragile than Aphthona, and have a much harder time extricating themselves from the plant debris. ​By the time we made our second trip to Idaho, in early July 2024, we were armed with multiple accelerators of two distinct designs, one focused on Aphthona and the other on Oberea. Both designs now work well on both species, but differ in the way that they facilitate the insects’ initial escape from the plant debris.​​
Two different designs of leafy spurge biological control "accelerators."
The Aphthona version to the left, the Oberea version behind on the right.
The second stage of sorting happens when you get your catch back to your (hopefully) shady workplace. It is here that the desirable biocontrol insects are separated from the rest of the bycatch. This is done with a device known as a “pooter,” or more technically as an “aspirator.” Using either lung power or, when available, a small vacuum pump, the biocontrol insects are sucked through a metal straw into a small collection vial. A line on the vial indicates the volume of 1,000 Aphthona, while the larger Oberea are counted individually. After collecting the appropriate number, the insects are then packaged into lots for distribution. Such hands-on sorting is required to avoid transporting and then releasing the unwanted bycatch species into the Yampa River’s riparian areas, which might potentially invite a host of new problems.
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Sucking up beetles efficiently is a skill that has to be learned by doing. And more doing. There's no getting around that. The story of YRLSP’s beetle collection successes has thus one of both experimentation and persistence.
Roddy and Jordan separating biocontrol insects from the bycatch in Idaho.
​​Of course, having an army of volunteers to collect and sort helps out, too. In 2024, a crew of thirteen individuals representing the YRLSP, Dinosaur National Monument, Colorado Department of Agriculture, Friends of the Yampa, and private landowners, travelled to Ashton, Idaho, where they were hosted by Kim Ragotzkie, contractor with the BLM. Over two days the group netted, sorted and packaged up 87,500 Aphthona and 2,450 Oberea, our largest collection of biological control agents to date.
Containers of Aphthona and Oberea collected in Idaho await transportation back to the Yampa Basin.
Biological Control Gallery
