Infected trees are Eastern Hemlock.
The tiny insect causes a white growth under the branches, with the tops of the branches looking like someone tossed white paint on the undersides.
The tree will turn brown and usually die, but treatments are available, if you want to save a model Hemlock.
Adelgid threads have appeared here at this forum since 2007.
Here's the real scoop from the USDA:
https://www.fs.usda.gov/detail/r9/ho...d=FSEPRD904421