Parasitoid vigor measured by female longevity, progeny production, and host destruction, is compared among cohorts from different populations of four Muscidifurax species: M. raptor Girault and Sanders, M. zaraptor Kogan and Legner, M. raptorellus Kogan and Legner and M. uniraptor Kogan and Legner, parasitoids of synanthropic flies. Different populations of the species are ranked according to their parasitization rates. Hybridization between populations usually produced an immediate post-mating parasitization depression in the female, with partial or full recovery occurring in randomly mated F₁ or F₂ progeny. Parasitization intensity approached an asymptote when females were 6 to 7 days old. Single matings were sufficient to guarantee female-biased sex ratios in progeny through 10 oviposition days, after which senescing females fertilized fewer eggs. Virgin females either approximated or exceeded mated females in parasitization activity. Preintroduction assessments of different parasitoid populations may be desirable for biological control to avoid postmating depression and the creation of inferior hybrids. Such assessments may also reveal cases where intercompatibility results in superior hybrids.