Please Report Sightings: Purple Loosestrife and Galerucella Beetles

By Lizzy Reitzloff, Stream Monitoring and AIS Coordinator

Purple Loosestrife (Credit to Addie Schlussel)

As many Wisconsinites might agree, residents have noted an unseasonably mild winter and high levels of flooding this spring and early summer. These changes in climate have noticeably affected the life cycles of some of the state’s invasives, including purple loosestrife (Lythrum salicaria). To better understand these changes and help the state’s purple loosestrife biocontrol programs, Rock River Coalition asks for local residents to report sightings of purple loosestrife and the Galerucella beetles that feed on them.

One purple loosestrife plant can produce over a million seeds, which can easily spread via wind or water and establish themselves in our local waterways. As a result, our native wetland species are outcompeted, reducing food sources for local wildlife, eliminating habitat for waterfowl, and impeding boat travel.

Most purple loosestrife biocontrol efforts rely on capturing and breeding Galerucella calmariensis beetles before re-releasing them into known purple loosestrife patches in the community. Originally introduced as a biocontrol species in the mid 1990’s the beetles have safely naturalized across the state. The beetles exclusively consume this invasive plant, making them an effective biocontrol method.


Galerucella beetle adults (Credit to Addie Schlussel)

How effective this biocontrol method is can change based on the timing of the Galerucella beetle and loosestrife life cycles. In an ‘average’ year at an ‘average’ purple loosestrife patch in southern Wisconsin, the plant sprouts in April and the beetles arrive in mid to late May to begin their feeding, mating, and egg-laying. This timing is typically good news for biocontrol efforts as it means the purple loosestrife has time to grow enough leaves to sustain beetle populations and that said beetles will be feeding on and stressing the plants prior to them producing seeds in late July to early September. However, changing climate patterns in the state, such as this year’s unseasonably mild winter and high levels of flooding this spring and early summer, has raised many questions and made this predator-prey relationship less predictable for conservation groups running purple loosestrife biocontrol programs. 

Galerucella beetle larvae (Credit to Addie Schlussel)

For example, there were some concerns with the early ground thaw in February that purple loosestrife might sprout sooner or the overwintering beetles emerging too early to find sufficient food, changing the timelines of biocontrol programs. However, the cold snaps that followed potentially killed off the plants’ top-growth and ‘reset’ its life cycle. Galerucella beetles have also been spotted, arriving early at purple loosestrife patches at the start of May, possibly feeding on the young plants before they could grow enough to sustain the beetles and their larvae. This change raises potential issues for both naturally occurring and human-driven biocontrol efforts, because if the Galerucella beetles don’t have enough plant material to lay their eggs, feed their larvae, and sustain their populations long-term, we may experience a beetle ‘die-off’ next year. However, it may be that the early feeding added even more stress to the plants to help reduce populations. The beetles are able to fly off to try to find new patches if needed.

If these year-to-year changes in climate continue to occur, the reliability of naturally occurring beetle predation on purple loosestrife may start to decline. Human-driven beetle-rearing and biocontrol efforts that can respond and adapt to these changes each year may become increasingly necessary in order to successfully repress these purple loosestrife populations long-term. To better understand the current state of purple loosestrife and beetle populations in the basin, Rock River Coalition is asking its readers to please report potential sightings of purple loosestrife and Galerucella beetles.

There are few ways to report them. There is a dedicated RRC online form for quickly recording volunteer sightings of both purple loosestrife and Galerucella beetles. Additionally, you can report any Galerucella beetle sightings to EDDsMapS, which is a “web-based mapping system for documenting invasive species and pest distribution”. Any questions can be forwarded to Lizzy Reitzloff, our AIS and stream monitoring coordinator at

This information will go a long way in helping purple loosestrife biocontrol programs to understand how the changing climate is affecting these two species and how staff can better adapt in the future. See photos and ID tips for purple loosestrife here at this WI DNR link and for Galerucella beetles here in this fact sheet.