Journey with Nature

Purple Loosestrife

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Purple loosestrife (Lythrum salicaria) first came to North America from Eurasia in the 1880s. There it was planted as a native ornamental in wetland vegetation. In the United States, it has escaped cultivation and invaded our wetlands and other wet areas such as lake edges and drainage ditches.

Even if you haven't heard of purple loosestrife, you've probably seen it. It is an easily recognized by its purple to magenta colored flowers of 5-6 petals and its long, square stems. In the peak of Indiana summers, it blooms in tall spikes creating quite a display.

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Though beautiful, once a wetland is invaded by this greedy plant it takes over, smothering everything in its path.  An area once teeming with frogs, fish, turtles and waterfowl is now void of animal life. Native flowers and plants including our delicate wild orchids are pushed out and the once diverse wetland becomes a shell of its former self. Only purple loosestrife remains and nothing else can make it in this purple tinged world.

Controlling Purple Loosestrife

Efforts to fight purple loosestrife and stem its invasion are costly, time-intensive and often unsuccessful. While herbicides are usually the weapon of choice, it is mostly effective on smaller populations and new infestations. For larger invasions of purple loosestrife, the Indiana Chapter of The Nature Conservancy has turned to an unlikely ally: non-native beetles.  

Though it sounds contradictory to purposely let loose an invasive species in a natural area, it turns out that these particular beetles only like to eat purple loosestrife. Galerucella calmariensis and G. pusilla have been used since the early 1990s in Indiana as biological control agents for purple loosestrife.  In numerous sites throughout the Great Lakes, biocontrol programs have been reported to have significantly reduced dense infestations, generally within five years of the initial release.

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Why these beetles? Both Galerucella calmariensis and G. pusilla's life cycles are tied to purple loosestrife. Their larvae feed on the growing tips and work its way down the plant as they get bigger. The plant loses more leaves as adult beetles continue to eat more as they lay their eggs on the loosestrife. The beetles were also thoroughly vetted in an extensive testing program to make sure they would not become pests of any other plant. Therefore, when the Purple Loosestrife populations decline, the beetles' will also, keeping things in balance. 


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