Every spring, since their 2000 introduction to Massachusetts, Galerucella calmariensis and G. pusilla beetles emerge from their underground winter shelters to feed on the young shoots of exotic, invasive Purple loosestrife plants, and soon after, to mate, lay eggs and die.

Introduced to the landscape to help control exotic, invasive Purple loosestrife (Lythrum salicaria), which has spread across North American wetlands, outcompeting native plants and making ecosystems unusable by some wildlife, these two species of small beetle eat and only will lay eggs on Purple loosestrife. Their appetites help to control the exotic, invasive plant when native North American organisms can’t do the job well enough.

These beetles naturally occur in the homeland of Purple loosestrife – in Europe and Asia. Because the beetles’ life cycles are so specific to Purple loosestrife, they do not degrade populations of native species.

Between 2008 and 2012, the Neponset River Watershed Association partnered with the MA Department of Conservation and Recreation – South Region to release these beetles at several treatment sites in state parklands. We released the beetles in a small wetland swale at Brookwood Farm on the Canton / Milton border, in the Blue Hills Reservation, and also in the northern Fowl Meadow, adjacent to Meadow Rd. in Hyde Park, within the Neponset River Reservation. In addition, we monitored one more study site in the northern Fowl Meadow, on the Milton side of the river. In total, our treatment focused on 25+ acres of Purple loosestrife-infested wetlands.

Each year, we monitored plant growth and Galerucella presence at our study sites – in the late-spring, before we had released the beetles, and then once again, in the early fall, after having released the beetles. Our monitoring data revealed the continued presence of the beetles at our study sites, year after year – which is a boon, as it shows that the beetles did indeed develop into a self-sustaining population (our goal). In addition, the monitoring results indicated that the beetles and their larvae continued to stress out the Purple loosestrife plants, causing the plants to focus more energy on restoring themselves than on producing seed (great news for the control of these exotic, invasive plants!).

While we have not done a structured evaluation of the project since 2012, there appear to be lasting benefits, as the beetles continue to significantly suppress the loosestrife without the need for ongoing intervention. Our hope is that over the years, as Purple loosestrife continues to be predated on by the beetles, a diversity of native wetland plants will grow in greater abundance and sustain a variety of native wildlife, including the endangered species previously recorded within our treatment sites.

Our project partner was the Mass. Dept. of Conservation and Recreation – South Region, and our initial project advisor was the Wetlands Restoration Program of the MA Office of Coastal Zone Management (now, the MA Division of Ecological Restoration).

Supported by funding from the Wildlife Habitat Incentives Program of the Natural Resources Conservation Service, the Corporate Wetlands Restoration Partnership, the Department of Conservation and Recreation Partnerships Matching Funds program, the NLT Foundation, the William P. Wharton Trust, and The Norcross Wildlife Foundation, Inc., and with the assistance of a strong corps of volunteers, we applied a biological control agent to reduce the exotic, invasive Purple loosestrife infestation in targeted wetlands.

For more information about these Purple loosestrife biocontrol beetles, contact NepRWA Executive Director, Ian Cooke at 781-575-0354 x305 or cooke@neponset.org.

May 14, 2013