The controlled release of Galerucella beetles has been completed. Observation of purple loosestrife still at Fresh Pond indicates that the beetle population is stable and will continue to control the growth of invasive purple loosestrife without additional beetle releases. No more Galerucella beetles will be purchased for Fresh Pond.
2006: The Purple Loosestrife Biocontrol project began in 2006 as a collaboration between the Friends of Fresh Pond and Cambridge Water Department.
2007: First population of Galerucella beetle purchased, reared, and released at Little Fresh Pond.
2008-2012: Additional populations of Galerucella beetles purchased and released to supplement existing adult populations. Observed damage to existing purple loosestrife populations.
2013: Existing adult population of Galerucella beetles adequate for purple loosestrife biocontrol. No new beetle populations purchased, continued monitoring to ensure efficacy of biocontrol project.
Purple Loosestrife, Lythrum salicaria, is an invasive wetland plant species native to Europe and Asia. It first appeared in North America during the 19th century, brought to this continent both in the ballast of ships and as an ornamental for gardens. This highly invasive plant has been observed in every state in the continental US with the exception of Florida. Purple loosestrife was first observed at Fresh Pond Reservation in the early 2000s, and had spread to inhabit shoreline space along every water body on the Reservation, as well as in several of the wetland bioswales at the beginning of this project in 2006.
As with any invasive species, purple loosestrife poses a serious risk to the ecological balance at Fresh Pond Reservation. Purple loosestrife alters the physical properties of wetlands by shading out smaller plants that would create a wetland understory and by altering the flow of water and sediments through the wetland. These alterations can limit the ability of wetlands to convert contaminants into more benign forms and recycle nutrients back into the ecosystem, which can negatively impact water quality.
Several control methods were tried with limited success before the Biocontrol project. Cutting the purple loosestrife causes the plant to sprout more stocks, leading to increased flowering. Pulling up the plant is very difficult, and if the entire plant is not removed, the remaining root system can still send out shoots. Herbicide is not a preferable option so close to drinking water source, especially as yearly application is necessary.
Biocontrol, in the form of the Galerucella beetle, seems to be the best choice for reclaiming wetlands on Fresh Pond Reservation. The Galerucella beetle was approved for use to control purple loosestrife populations by the USDA in 1992.
Galerucella beetles are native predators of purple loosestrife in Europe. Of the 100 insects initially investigated for use as a biocontrol agent, Galerucella calmariensis and G. pusilla are two of the 4 insect species currently used in the US to control purple loosestrife. The beetles live and breed exclusively on purple loosestrife, and during host specificity testing, starved rather than eat associated wetland vegetation. The Galerucella beetle goes great distances to find purple loosestrife because it will not mate or lay its eggs on any other species of plant. The beetle will occasionally nibble on other vegetation once purple loosestrife has been depleted, but will ultimately move on, leaving the native vegetation intact. This makes this beetle an excellent biological control species.