The associations of various species of Drosophila with certain solitary endoparasitic wasps provide exceptionally good experimental systems for studying the population dynamics of the coevolving traits of host resistance and parasitoid virulence. This review examines the interactions between Drosophila melanogaster and its larval endoparasitoids (e.g., Leptopilina boulardi, Leptopilina heterotoma, Asobara tabida, and Ganaspis mellipes) to illustrate the nature and genetic bases of the counterstrategies used by the combatants in their struggles to protect their own homeostatic mechanisms. In addition, we discuss some of the cellular and humoral mechanisms involved in insect innate immunity and their associated signal transduction processes. These studies highlight the similarities that exist in the innate immune systems of vertebrates and invertebrates. none