Purple loosestrife (Lythrum salicaria) is an aggressive invasive plant that can take over wetlands and alter the functioning of the areas it invades.
In 1994, the State of Michigan joined five other states and Ontario in a USDA-guided biocontrol program and released thousands of non-native leaf-eating Galerucella beetles into native wetlands. If that sounds like a bad thing, this program has since been considered one of the better success stories in the realm of biocontrol.
In 1997 Matthaei Botanical Gardens became a cooperating site for a nationwide release and monitoring program for the control of purple loosestrife, during which staff released 35,000 Galerucella beetles into the natural areas of Matthaei.
The good news is that we still have the beetles, says Matthaei-Nichols Field Services Manager Jeff Plakke. “They are still present on the loosestrife around Willow Pond. They fluctuate from year to year with the loosestrife population as well as environmental conditions, that is, flooding vs. drought,” Plakke explains.
Matthaei-Nichols staff have collected adults from these plants and introduced them to other populations of loosestrife on the property to help control the plant. The insects help keep the loosestrife from developing very large, homogeneous stands, Plakke adds, but the beetles alone cannot eradicate a stand of loosestrife.
“For additional control, we sometimes use targeted treatments of aquatic-approved herbicide and/or digging and hand removal if we feel the cost of the chemical use or physical disturbance is worth the potential benefit,” according to Plakke. The long-term goal, he says, is to manage the loosestrife population—not eradicate it, since this is impractical or unrealistic—so that many of our native wetland species can thrive and recolonize their former ground.
Continue reading the fascinating story of a non-native being introduced to control a non-native, and how the strategy has been successful. Katie Ferran, a Matthaei-Nchols intern, wrote the original story in 2019 for our blog.
Original story from 2019 by student intern Katie Ferran:
“If it’s pretty, pull it,” a volunteer supervisor with the San Antonio River Authority once joked with me as we proceeded through a workday to maintain a native wildflower bed alongside the river walk. It broke my heart a little to yank out the poppies growing there, but it was for the best, I was told.
Pretty, yes. But most invasive plants that pose risks to native plant communities were brought to the continental United States as ornaments to augment the aesthetics of manicured settings, like gardens and yards. Thus, invasive species are often very beautiful, which can sometimes make the conservation of natural areas feel like a step in the wrong direction when it comes to preserving the beauty of the outdoors. To clarify, an invasive species is classified as an organism that has established itself outside of its home range, and is actively reducing the populations of native species, either through competition or predation.
Not to confuse the issue, but sometimes an invasive need not be foreign. If a native species is allowed to grow unchecked, it can behave like a non-native invasive and do serious damage (think white-tailed deer). Additionally, not all alien species are considered invasive if they more or less “fit in” with the community they are introduced to. An example of a benign non-native would be the honeybee, which was introduced to the Americas during the 1600s. But in most cases, an invasive is an invader in some respect, and means of controlling them have been the source of enormous volumes of research, trial and error, and sometimes disaster.
Introducing the Beetles
In 1994, the State of Michigan joined five other states (and Ontario) in a USDA-guided biocontrol program and released thousands of non-native leaf-eating beetles into native wetlands. If that sounds like a bad thing, this program has since been considered one of the better success stories in the realm of biocontrol. The beetles were released in an effort to control purple loosestrife (Lythrum salicaria L.), a beautiful stemmy plant from Eurasia that ended up notorious for choking out wetland plant communities and altering the functioning of their invaded areas.
Initially planted for ornamental appeal and for beekeeping purposes, the “purple plague” spread all throughout the continental United States (with the exception of Florida) and into Canada, prompting the International Institute of Biological Control (IIBC) to begin a search for a biological management plan in 1985. This method of invasive plant management involves introducing a pest that will specifically target the plant with the goal of significantly reducing its population. Mechanical management (the physical removal of the plant) and chemical management (the spraying of herbicides) were found to actually increase the rate of purple loosestrife spread by creating disturbed conditions ideal for new growth, and the IIBC instead isolated four ideal species for biocontrol: two leaf-eating beetles in the Galleria genus, one root-eating weevil, and two flower-eating weevils. The University of Michigan Matthaei Botanical Gardens became a cooperating site in 1997 for a nationwide release and monitoring program for the control of purple loosestrife, during which staff released 35,000 Galerucella beetles into the natural areas of Matthaei.
Purple loosestrife (Lythrum salicaria L.), a beautiful stemmy plant from Eurasia that notoriously ended up choking out wetland plant communities and altering the functioning of their invaded areas.
A Well-Meant Remedy Goes Bad
If all of this makes you a little nervous, you’re not alone. One need only look at the cane toads of Australia to see how badly wrong biocontrol can go. In the 1930s, sugar cane farmers were suffering under a plague of grey-backed cane beetles, which subsequently led to the release of roughly 100 South American cane toads into Northern Queensland. Long story short, the cane toads did their job and then went above and beyond by decimating all the native wildlife in their path, including small mammals, birds, and lizards.
The key to successful biological management of an invasive species is picking a pest that is a specialist: it will only feed on the target species and nothing else. Otherwise, the introduced pest may end up being even more of an ecological disrupter than the original target species.
This has not been the case at Matthaei, nor for Michigan as a whole. The dedicated work of University of Michigan student Asli Aka and later Rebecca Rogers, along with Matthaei’s then-associate director Brian Klatt, monitored the purple loosestrife and Galerucella beetle populations for the better part of decade, and found promising results. In other parts of the state as well, previously unchecked populations of purple loosestrife became more and more riddled with holes, their ranges generally shrinking. Research here at the University of Michigan and Michigan State have not found any negative ecological consequences of the beetle’s introduction; it seems this specialist is not yet interested in branching out to other plants.
But as I get further into the history of the purple loosestrife and the Galerucella beetle, I find that the “why” can get a little lost in the shuffle. Why is the purple loosestrife so bad, and if so, why are we settling with a method of control that does not truly remove the plant from our landscapes? There is actually still a great deal of debate today as to whether the conservation ecology community should continue its war on invasives the way it has for the past several decades.
In the 70s and 80s, as conservation really began to grow as a discipline, the paradigm on which all practice has since been based was that native communities are better than communities disrupted by invasives. One could argue that this is generally true through the lens of ecosystem functioning and the cultural and societal values of particular landscapes, but with globally changing temperatures, it may not be so simple. The home ranges of many plants are not remaining static. Plants and animals are moving north and to higher altitudes as the world gets hotter and drier. Does that make them invasive, and therefore in need of eradication? In this way, some have raised concerns that if we institute a strict “native only” strategy, we will actually be doing more harm to global biodiversity than good. The world is changing, and it’s unclear how to help make those changes beneficial for the health of the environment and the safety of the public.
Objectively, however, the purple loosestrife is not just a plant struggling to find a new home range. For many years, it was omnipresent across the country, and it ain’t going away anytime soon. Ships from Europe helped it make the trip to North America, and by invading wetland communities, the loosestrife actually changed the way entire wetlands functioned. As many Michiganders may know, wetlands are instrumental in watershed regulation and preservation. In other words, if you want to have clean drinking water, you had better keep your wetlands happy.
If you want to get into a semantic-ridden argument about why weeds and invasives shouldn’t be demonized for simply existing, I wouldn’t start with defending the loosestrife—it’s genuinely bad. What I would defend instead is the Gallerucella beetle. Traditional opposition to biocontrols are usually borne of a mistrust for the outcome of intentionally introducing another foreign species to an already disturbed environment (remember the cane toad?). This is the attitude that I believe needs changing. What makes the purple loosestrife a problem is not that it is an alien, but that it is disruptive. These are not mutually exclusive characteristics; there are natives that are disruptive to beneficial plant communities, and there are non-natives that fit in just fine.
Additionally, an invasive need not totally disappear from a landscape to stop hurting it. A concept gaining traction in invasion ecology circles is “naturalization,” or the process by which a native community eventually finds a way to control the unchecked growth of an invasive. Once the invasive has an enemy that limits its survivorship, it begins to behave more like a member of the community, and its population stabilizes. The difficulty is, we are still unsure how long this process could take, and if it can even happen if the invasive proves to be too prolific.
That is where the success story of the purple loosestrife and the Gallerucella beetle looks to be highly encouraging. It represents a management option that is more concerned with the functionality and health of an ecosystem, not just its native-ness. We will likely see more management programs like this in the future, where the global movement of species grows more inevitable, and the manual or chemical options grow less and less realistic. The world is changing, and our understanding of what is right and wrong with the land will change, too.
Katie Ferran is a second-year graduate student at the University of Michigan’s School for Environment and Sustainability, seeking a master’s degree in Natural Resources and the Environment with a concentration in Conservation Ecology. She grew up in Fayetteville, Arkansas, and earned a Bachelor’s Degree of Science in Environmental Science at St. Mary’s University of San Antonio, Texas. Katie is interested in invasion ecology and forest pathology, and spends her free time doodling and enjoying the outdoors with her fiance, Scott.
The cane toad (above) was released in Northern Queensland, Australia in the 1930s to control the population of grey-backed cane beetles. The cane toads did their job and then began decimating all the native wildlife in their path, including small mammals, birds, and lizards. Photo by Queensland Times (Australia)
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