Abstract
A systematic study of the genus Ormyrus (Chalcidoidea, Ormyridae) was conducted based on the morphology and biology of the terminal-instar larvae of ten west European species that are parasitoids of gall wasps and gallflies of the families Cynipidae, Eurytomidae and Tephritidae. The first detailed descriptions are provided of the terminal-instar larvae of these ten species using SEM images to illustrate diagnostic characters with systematic values. A key is provided for the identification of ormyrid larvae associated with galls in Europe, which is based particularly on characters of the head, mouthparts and mandibles. Although only limited informative variation in body shape was found, the setation of the head provided several characters of potential taxonomic value. The larval biology of the ten ormyrid species inhabiting different galls is also summarised. Although Ormyrus larvae are usually solitary idiobiont ectoparasitoids of the host larva of various gall-inhabiting insects, evidence of secondary phytophagy was observed in some species.