April O'Neil / news@WHMI.com

Michigan’s invasive species watch list was recently updated to include two new species, and remove another.

Mountain pine beetle, a deadly threat to pine trees, and water-primrose, a fast-spreading aquatic plant, have been added to the watch list due to threats they pose to native ecosystems and industry.

European frog-bit, originally listed in 2011, is now considered established in the state, and has been removed from the list of species of immediate concern, according to the DNR.

The Mountain pine beetle has been characterized as the most aggressive, persistent and destructive bark beetle in the western U.S. and Canada. Hot, dry summers and mild winters in these areas have led to the beetle’s unprecedented population growth and range expansion, moving it ever closer to Michigan.

Because it attacks most species of pine, the invasive beetle could have widespread effects in the state.

“White and red pines are primary species in our forest ecosystems, and jack pine serves as critical habitat for the Kirtand’s warbler,” said Susie Iott, invasive species program specialist with the Michigan Department of Agriculture and Rural Development. “If mountain pine beetle were to become widely established in Michigan, it would cause severe losses across multiple industries, including timber products, plant nurseries and tourism.”

Because the beetle can be transported on infested pine logs, firewood and other similar commodities, MDARD issued an exterior mountain pine beetle quarantine in 2020 to regulate the movement of all firewood and any pine products with bark attached from areas of the western U.S. and Canada. Since mountain pine beetles are tiny and live under bark, they often are detected by the presence of many popcorn-like lumps of pine pitch, called “pitch tubes” on pine tree trunks. Pitch tubes can be brown, pink or white and are created as the tree attempts to push out an entering beetle.

Water-primrose (pictured) is a group of very similar non-native plants that are invasive in wetland ecosystems. Water-primrose is quick to establish and spread in dense mats within wetlands and shoreline areas, outcompeting native species and making boating and water access difficult.

Three known populations, two in the greater Detroit area and one one the west side of the state, indicate the species can survive and thrive in Michigan’s climate. Once established, the DNR says water-primrose can be very difficult to remove, making early detection critical.

“Water-primrose is not a regulated species in Michigan. Though not common in trade, it was likely introduced through the landscape or water garden pathway,” said Bill Keiper, aquatic biologist with the Department of Environment, Great Lakes, and Energy.

Invasive water-primrose can be found along the water’s edge or floating on the water. Plants grow upright to 2 feet in height and also spread horizontally. Look for reddish stems, willow-like or spatula-shaped, dark green leaves and a showy, yellow flower with five or six petals.

The good news? After a recent review of European frog-bit, an invasive aquatic plant, it was determined that the plant no longer met watch list criteria due to its establishment in many areas of the state. European frog-bit still retains its prohibited status, making it unlawful to possess, introduce, import or sell in Michigan. State and local management efforts for European frog-bit will continue despite the status change.

The public is encouraged to look for and report potential infestations of mountain pine beetle and water-primrose.

When reporting watch list species, the DNR says to use the Midwest Invasive Species Information Network online reporting tool (link provided) or download the MISIN smartphone app and report from your phone.