Here is some information on Pear Slugs . They love to go after the leaves of pear and cherry trees. Due to deep snow the rabbits were chewing off branches and bark well above the plastic strips I had protecting the stems. I have had problems with aphids, pear slugs as well as catipilars. It also works on catipilars but not as well.
Soap is a contact poison for many insects and it leaves no residue.
Do NOT spray the trees in hot weather. Pick a cool time and rinse the trees after. Pear slugs are a translucent to dark slug that eats the leaves of trees. A solution of vegatable oil with a bit of soap makes an insecticidal soap spray. Aphids seem to primarily go after my plum trees or apple trees and they prefer new leaves over all else.