In the present paper, by simple probability consideration, the incompatible, compatible, and independent features of predation or parasitoid behaviours between two natural enemy populations are distinctly considered.The precise probability implications are given for the predation or parasitoid rate in several mathematical models recently developed by Hassell, May and Beddington. And, mathematical models of nearly realistic interactions between two natural enemies (P,Q) and one pest (N) are presented as in t...