I have seen using burlap and folding it over. Tie it around the tree using bungee cords and they crawl up the trunk and go under the burlap and seem to stay there. Then you can burn them. Either shake them into a fire or burn the burlap and all.
I did see on Channel 16 tonite of a house that was covered with them. We don't have that many near our house but I kill everyone I see.
First unless the trees are really big I would just get a ladder out and go about hand picking them to remove them from the tree rather then spraying. Its not that hard and doesn't take too long. Dont need to get every one, just enough so the tree can still have leaves to produce trees. Then deal with the truck as mentioned above.
Second. I've never heard of Gypsies feeding on fruit trees? Are you positive their Gypsies and not tent catapillars?