Equicare Simplifly with Larvastop, 50 Pound by Farnam. $226.49. Reduces fly populations by 97-100%.. Larvastop, containing fly growth regulator Dimilin, breaks the fly life cycle. Highly palatable - just add to feed. Reduces fly populations by 97-100%. Simplifly with Larvastop is a highly palatable feed additive to prevent the development of stable flies and houseflies in the manure of treated horses.. Save 22% Off!