They won't build a resistance to neem as far as I know. Neem basically sterilizes mites. www.hidhut.com used to have very small vials for like $10, also of Floramite, but now only carry an 8 oz. size for about $135...which will last a lifetime...lol.I'm going to get it but I won't use it unless these mites build up a resistance to Neem.