I know the best stuff to try and it shouldn't harm the wax or finish on the boats.
It's call " Bug Stop", Menard's carries it.
My mom sprays it on her house every spring and it stops lake flies, spiders, gnats, you name it.
It won't harm animals or the environment, and it's bio-degradeable. It's actually for plants so you know it's safe.
Wash the boat with soap and water rinse and spray the " Bug Stop" it doesn't even leave spots............