Go to the MSU gypsy moth website and download the bulletin about using Bt for GM control.  Bt is a bacteria that can be sprayed aerially or from the ground. It only works if caterpillars eat leaves that have the spray on them - just walking over sprayed leaves or bark has no effect.  Bt is not toxic to anything except caterpillars that eat sprayed leaves (not pollinators, or pets or birds or people...).  You may be able to find aerial applicators in the SW region of the state who are still able to apply Bt.  Most of those guys get booked up well ahead of spray season - we are right in the thick of Bt sprays currently.  I attached the list of aerial applicators that were licensed in MI as of 2021 - that's the most up to date list I have.  Otherwise, you can have an arborist spray your trees from the ground with a high pressure nozzle and tank.  THere is a product called Acecaps that you can use on oaks that are being defoliated.  It is a general use product - you can buy it online.  You drill thru the bark and just into the sapwood of the tree and shove a capsule in.  Then you go over and up, drill another hole, and so on.  FOllow the label - it will have all the info you need.  Finally, you can put a high pressure nozzle on your garden hose and just blast all the caterpillars you can reach.  Step on any that fall to the ground.  Might not be super effective but it can be good therapy when you are sick of the caterpillars. The warm weather means caterpillars are developing fairly quickly.  Feeding should be wrapped up by 4th of July and hopefully a bit sooner down in your area.