Oviposition behavior was used to determine if handling time was a reliable indicator of host suitability for oviposition by the ectoparasitic wasps, Nasonia vitripennis (Walker) and Muscidifurax zaraptor Kogan & Legner, on pupae of Sarcophaga bullata Parker, the black blow fly, Phormia regina (Meigen), and the house fly, Musca domestica L. Oviposition behavior of both parasitoids was composed of a series of stereotypic and interdependent events or phases. The duration of behavioral events preceding puparium penetration was influenced by host species, indicating that host recognition depends on some external cue associated with the fly puparium. Total handling time was stereotypic regardless of host species or the number of eggs laid on a host, suggesting that the amount of time invested by N. vitripennis and M. zaraptor in oviposition does not predict clutch size or host preference. When N. vitripennis and M. zaraptor were held together at low host densities, females of N. vitripennis reacted aggressively and interfered with all oviposition attempts by M. zaraptor. Aggression by N. vitripennis toward M. zaraptor subsided when host density was increased, presumably because this was a less competitive situation.
