Although the enemy release hypothesis forms the theoretical basis for classical (=importation) biological control of invasive pests, its core assumptions are not always examined. This could contribute to unrealistic expectations for some biological control programs. In this paper we examine the assumptions that: (i) enemy release has contributed to the invasive nature of four exotic pentatomids in North America; and (ii) classical biological control with egg parasitoids has been or will be successful in reducing populations of these pests below economically significant levels. We use simple stage-structured matrix models to demonstrate that it may be easy to overestimate the contribution of egg parasitism alone to a reduction in stink bug population growth and discuss what realistic expectations might be for success of biological control in the context of integrated pest management programs.