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Indiana Department of Natural Resources

Entomology & Plant Pathology > Regulatory & Scientific Information > Purple Loosestrife > Biological Control of Purple Loosestrife Biological Control of Purple Loosestrife

Purple loosestrife has become such a pest because it came to North America without the insects that control it where it is native. Releasing the insects that control loosestrife in Europe can bring it under control. Between July 1998, and July 1999, the amount of purple loosestrife around the boat ramp at Pleasant Lake in St. Joseph county decreased dramatically.

Purple Loosestrife - 1998
Purple Loosestrife - 1998

Purple Loosestrife - 1999
Purple Loosestrife - 1999

The insects that accomplished this are two small leaf eating beetles, Galerucella calmariensis and G. pusila. Before being released, they were carefully tested to make sure they would not become a threat to any other plants.

The insect's entire life cycle is tied to purple loosestrife. The larvae start feeding by destroying the growing tips. As they get bigger, they move down the plant, reducing the leaves to skeletons. The adult beetles continue to eat even more leaves as they lay eggs on the purple loosestrife.

Adult Galerucella
Adult Galerucella

These brown stalks show how large and tall the purple loosestrife grew in 1998.

These brown stalks show how large and tall the purple loosestrife grew in 1998.

Without competition from purple loosestrife, native plants, and the wildlife that depend on them, can recover.

Galerucella were first released at Pleasant Lake in 1996 through the joint efforts of IDNR's Division of Entomology & Plant Pathology and Division of Nature Preserves.  So far they have been released at about 40 sites across Indiana. We expect Galerucella to eventually spread to all wetlands where purple loosestrife has spread. 

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