Genetic benefits from mating with multiple males are thought to favor the evolution of polyandry. However, recent evidence suggests that nongenetic paternal effects via seminal fluid might contribute to the observed effects of polyandry on offspring performance. Here we test this hypothesis using the field cricket Teleogryllus oceanicus. Using interference RNA we first show that at least one seminal fluid protein is essential for embryo survival. We then show that polyandrous females mated to three different males produced embryos with higher pre-hatching viability than did monandrous females mated with the same male three times. Pseudo-polyandrous females that obtained sperm and seminal fluid from a single male and seminal fluid from two additional males, had embryos with viabilities intermediate between monandrous and polyandrous females. Our results suggest either that ejaculate mediated paternal effects on embryo viability have both genetic and nongenetic components, or that seminal fluids transferred by castrated males provide only a subset of proteins contained within the normal ejaculate, and are unable to exert their full effect on embryo viability.