Chigger killing environments

When I was in the army and out and about in the field all the time I was taking Brewer’s yeast as a supplement. And I was never bothered by mosquitoes or chiggers while everybody else was eaten up.  I did find mosquitoes would still fly around and buzz you, but they wouldn’t land and bite and there were times I put earplugs in to sleep just to not hear the buzzing. Your mileage may vary. Also, I noticed many people in the army also did not know the rule of leaves of three let it be, and poison ivy was a problem for them.