none We tested the hypothesis that the host larval instars preferred by the adult female of two parasitoids of the spruce budworm, Choristoneura fumiferana (Clemens), also are the most suitable for immature survival, growth, and development. The hypothesis was supported for the tachinid Winthemia fumiferanae Tothill but not for the braconid Meteorus trachynotus Viereck. W. fumiferanae preferred the sixth over the fifth host instar for oviposition; the sixth instar also was the most suitable for the traits investigated. In addition to host instar, host sex also influenced larval development and pupal weight of this parasitoid. M. trachynotus preferentially approached sixth instars of the host, but second to sixth instars were attacked with equal frequency. Survival of this parasitoid was high in all instars tested, but development time from egg to pupa decreased and cocoon weight increased in older instars.