WD40. Years ago a faculty member recomended i try wd40 ( a thin petrolium product) for my hunting related bites. It worked so well I have been using it in my practice for decades. It seems to sufficate the buggers but it also has an anti-itch effect.
Sulphur. By far, the most effective and time-proven repellent for chiggers is sulphur. Chiggers hate sulphur and definitely avoid it. Powdered sulphur, called sublimed sulphur or flowers of sulfur, is available through most pharmacies. Dust the powdered sulphur around the opening of your pants, socks and boots. If you plan to venture into a heavily infested area, powdered sulphur can be rubbed on the skin.