Survival of the gregarious ectoparasitoid Mastrus ridens on codling moth, Cydia pomonella, and non-target species

Survival in the laboratory of Mastrus ridens Horstmann (Hymenoptera: Ichneumonidae) reared on larvae of Cydia pomonella (Linnaeus) (Lepidoptera: Tortricidae) and five species of non-target Tortricidae was compared. Clutch size (numbers of eggs per host larva) and survival were higher on codling moth than on non-target species, and most adults reared from non-target larvae were smaller. F₂ generation M. ridens adults reared on Argyroploce chlorosaris Meyrick and Cydia succedana (Denis and Schiffermüller) larvae were also small, with a sex ratio skewed to males. Few parasitoids survived, and they did not appear to have adapted to the non-target species on which their parents were reared. When M. ridens eggs were immediately removed from venom paralysed larvae, no codling moth larvae but most non-target larvae died within a few days. It is suggested that the host-paralysing venom of M. ridens is adapted to ensure the survival of codling moth larvae and is lethally maladapted to non-target species, such that it might be possible to determine ectoparasitoid host range by biochemical or physiological tools that characterise venom or prey response, respectively.