State Officials Work to Slow Spread of Hemlock Wooly Adelgid

State Officials Work to Slow Spread of Hemlock Wooly AdelgidThe Department of Agriculture and Rural Development has issued a quarantine on hemlock tree movement in four counties in Western Michigan. The order came after state officials discovered a significant infestation of an aphid-like invasive species in Allegan, Muskegon, Oceana and Ottawa counties.

Native to Japan, the hemlock woolly adelgid has been problematic in eastern states for decades, but the destructive insects have only recently raised serious concerns in Michigan. Some experts have attributed the sudden outbreak to a pair of back-to-back mild winters that allowed the adelgids to reproduce freely and spread to new areas.

As their name implies, hemlock wooly adelgids are picky eaters that only target hemlock trees. The insects are all female, and they reproduce asexually. This unique trait allows them to start new colonies easily and grow their numbers rapidly. Once an adelgid is born, it may spend its entire lifespan on the same branch of hemlock tree.

The adelgids feed on the trees by using their long, straw-like mouths to suck nutrients out of hemlock needles and branches. Once they’ve attached to the trees, the adelgids typically stay in the same place until they die. As the insects feed, they secrete fine strands of wax that form protective cocoons around their bodies. Once this wax case is complete, the adelgids lay eggs and the life cycle begins again. Juvenile adelgids can crawl to new locations on the tree, or spread to other trees via wind, birds and other animals.

Michigan officials are urging residents who spot white, waxy materials on hemlock needles to refrain from disturbing the branches, and to report the potential infestations to the Department of Agriculture and Rural Development at By isolating these infestations, the department hopes to prevent widespread damage to Michigan’s 170 million hemlock trees.