Ormyridae

Ormyrid wasps

HYMENOPTERA > APOCRITA | Parasitica > Chalcidoidea > Ormyridae

Ormyridae is a small family of parasitoid or hyperparasitoid wasps associated with plant galls.

Worldwide there are just over 150 species in five genera that are separated into three distinct subfamilies; Asparagogiinae with four species that form galls on Asparagus or a particular type of heather (Ericaceae); Hermadinae with one species that is only found in South Africa, which is another gall former; and Ormyrinae, with two species in the Ouma genus recorded from Africa, but where the biology is unknown, and then all the remaining 140+ species in the Ormyrus genus, which are parasitoid wasps of the gall-inducing insect larvae, rather than gall-formers in their own right.

They are represented in Britain by four species; Ormyrus gratiosus, nitidulus, papaveris and pomaceus. Their status is difficult to determine as they are so poorly recorded. At the time of writing there were just 27 records on the NBN Atlas database, with the most southerly verified sighting coming from North Somerset. The most frequently recorded species is Ormyrus nitidulus, as featured here.

As members of the Ormyrinae subfamily, these particular species are usually referred to as Ormyrine wasps rather than using the collective family name, as the definition confirms the fact that they are true parasitoids as noted above.

Ormyrus nitidulus larvae are idiobiont ectoparasitoids primarily associated with various oak gall wasps especially those of the Andricus and Cynips genera, but also one species of gall midge, Oligotrophus bergenstammi. The adults can be seen from late spring to early autumn and, not surprisingly, will most often be encountered on, or in the vicinity of, oak trees.

For future reference, the larvae of Ormyrus gratiosus is associated with Tephritidae (Urophora) and Cynipidae (usually Aylax spp.) in flower heads of Asteraceae plants, Ormyrus papaveris with the galls of Aylax papaveris in the seed capsules of poppies (Papaver) and Ormyrus pomaceus, similar to Ormyrus nitidulus, but especially with Andricus, Biorhyza and Neuroterus cynipid gall wasps on oak trees.

They are easily distinguished from other species of chalcid wasps by their distinctive appearance. Female Ormyrus nitidulus are usually slightly larger than the other species, typically with a body length of around 4-5mm, compared with the male, which is about half the size. The body is hunched, metallic blue or greenish-blue, with abdominal segments that have a surface sculpture of coarse pits when viewed from above. Whilst Ormyrus nitidulus could be confused with Ormyrus pomeaceus, they can usually be separated from the other two species simply by where they're found, but on closer inspection they have a keel along the top of the abdomen that is not present in Ormyrus gratiosus or Ormyyrus papaveris. There are also differences with regard to the structure of the antennae. More importantly, Ormyrus nitidulus can be distinguished by its long, upturned epipygium, whereas in Ormyrus pomaceus it's much shorter and only weakly angled.