Raising Beetles to Tackle an Invasive Plant
A perspective on biocontrol efforts in the estuary contributed by Kate McCall.
Phase 1: May 2 was a typical gray, chilly, spring day in Superior, Wisconsin. On this day, a plan was put into action in collaboration with Douglas County Water Resources. Working together at the Lake Superior Reserve the 2022 biocontrol effort to combat the spread of purple loosestrife began. Purple loosestrife is an invasive plant in the estuary. The day involved planting purple loosestrife that had been pulled from the shoreline into plastic tubs and kiddy pools. Meanwhile, others were setting up a mass-rearing tent of thin netting. We then put these tubs and pools inside the tent so that the newly planted purple loosestrife could grow into big, leafy and healthy plants. That sounds odd, doesn’t it? With purple loosestrife being a threat to native wetland plant diversity throughout the estuary, why would we be growing it? Read on for the answer!
Phase 2: June 13 was an even chiller, lake-wind kind of day. Still, the day found another group of us gathering on Barker's Island to collect Galerucella beetles. These leaf eating “Cella” beetles prefer purple loosestrife to other plants. When they chew up the plant, they damage its ability to thrive and reproduce. We were collecting these beetles to use their offspring to reduce the purple loosestrife population in targeted parts of the Lake Superior Reserve. This is called biocontrol, the use of one species to manage another without the use of chemicals. We cut the top off plastic liter bottles then turned the top back down into the bottle to create our beetle catchers. We collected about 450 beetles off purple loosestrife around the shores of the Lake Superior Reserve. We took them into the mesh tent and placed 6-8 beetles per plant. Thus, the mass beetle rearing began.
Phase 3: July was a temperamental month due to spates of more chilly, gray weather. Initially we thought the Reserve’s “great beetle release” might happen around the Fourth of July. Instead, the beetles were ready much later, toward the end of the month when the sun came out and warmed things up. That’s when the beetles finally grew in great numbers and were hungry! On July 28, volunteers released approximately 5,000 beetles near Hog Island wetlands and Loon’s Foot Landing, Superior. On July 29, about 3,000 beetles were released at Barker’s Island stormwater pond, but the bulk of the tent-reared beetles were released in several locations in Allouez Bay, near Lot 1 of Wisconsin Point. The collaborative efforts produced about 25,000 beetles to munch away at three populations of purple loosestrife.
For more information on purple loosestrife and how to identify it go to https://Dnr.wi.gov/topic/Invasives/fact/PDFs/loosestrife.pdf.