Two different life-history strategies determine the competitive outcome betweenDirhinus giffardii(Chalcididae) andPachycrepoideus vindemmiae(Pteromalidae), ectoparasitoids of cyclorrhaphous Diptera

Abstract

AbstractDirhinus giffardiiSilvestri andPachycrepoideus vindemmiaeRondani are solitary parasitoids attacking puparia of many cyclorrhaphous flies. They are not typical ectoparasitoids, as they feed on host pupae within puparia that develop from the exoskeleton of host larvae.Dirhinus giffardiidid not kill its host until the parasitoid egg developed into a larva, whileP. vindemmiaepermanently paralysed its host at the time of oviposition. As a result, ovipositing into a young host puparium (< 1 day old) in which the host pupa has not yet fully formed resulted in complete death of offspring inP. vindemmiae, butD. giffardii, although suffering higher mortality than in older host puparia, still showed a level of successful development. In a choice experiment, both parasitoids preferred to attack 2- to 3-day-old puparia in which the host pupae had fully formed, rather than 1-day-old host puparia.Pachycrepoideus vindemmiaealways prevailed in competition because it injected venom that not only paralysed the host, but also caused the death ofD. giffardiilarvae in multi-parasitized hosts.Dirhinus giffardiipreferred to attack unparasitized hosts rather than hosts previously parasitized byP. vindemmiae, whileP. vindemmiaedid not show a preference between unparasitized hosts and hosts previously parasitized byD. giffardii.