Host selection behaviour in Mastrus ridens, a gregarious ectoparasitoid of codling moth, Cydia pomonella

The host-acceptance and oviposition behaviours of Mastrus ridens Horstmann (Hymenoptera: Ichneumonidae) on cocooned codling moth (Cydia pomonella (Linnaeus) (Lepidoptera: Tortricidae) and non-target tortricid larvae were characterised. Acceptance appeared to result from analysis of kairomones in the silken cocoon and not from the size or movement of the larva within. No larva of three non-target species (Planotortix octo Dugdale, Grapholita molesta (Busck) and Cydia succedana (Denis & Schiffermüller)) was recognised by M. ridens, but a few larvae of Ctenopseustis obliquana Walker and Argyroploce chlorosaris Meyrick were accepted and eggs laid. Scanning electron micrographs of antenna and the ovipositor sheath revealed sensilla likely to be involved with host recognition. It appears that a female M. ridens can only locate a host within a habitat by encountering specific, contact chemical cues and by acoustical sounding. Generally, New Zealand’s native insects are not at risk because they are simply not recognised as possible hosts.