Attacking the hemlock attackers
On a hot summer day, I was enjoying a few quiet moments next to a stream in Sullivan County, NY. I saw some ebony jewelwings flutter near the stream in courtship flight, and in the stream, there was the occasional brook trout. Even though the temperature was warm, the habitat around me had moderately cool temperatures due to a lot of shade provided by the many Eastern hemlock trees that formed a canopy over the stream and the gorge just downstream.
Just a few hundred yards away from the stream, there was an area approximately an acre in size where hemlock trees were growing, but a lot of sun was hitting the ground and a few understory plants; the hemlocks were dead and had no needles. A close look at some living hemlocks nearby revealed what looked like tiny cotton balls at the base of the green needles that are indicative of a non-native insect pest, the wooly adelgid.
Over the years, the wooly adelgid has spread from the south to affect hemlock stands in our region. The loss of hemlock stands and resulting loss of habitat threaten fauna and flora unique to hemlock forests. As hemlock stands are frequently found around stream environments, the cold-water fishery (trout) would be jeopardized, as water temperatures grow too warm due to the lack of shade. A resultant increase in soil erosion due to tree loss would also threaten stream water quality.
This pest has proven difficult to eradicate. Aerial application of insecticide is not effective; trees have to be treated individually by injection, which is not practical for large stands of hemlock. Over the course of the last decade, several state and federal agencies have been experimenting with biological controls in the form of several species of predatory beetles that feed on wooly adelgid. One of these shows particular promise: the Sasajiscymnus (formerly Pseudoscymnus) tsugae, a form of ladybird beetle that was imported from Japan
S. tsugae is host-specific; it will only feed on wooly adelgid. Its lifecycle closely syncs with the lifecycle of its host, and is well suited for treating more than a single tree at a time. Because it winters well in cold environments, one introduction should be effective for several seasons. As this beetle is itself an insect, care should be taken in using any other chemical insecticides in the area. A source for this predator beetle that markets to individuals can be found at tree-savers.com/