HYMENOPTERA > APOCRITA | Parasitica > Diaprioidea > Diapriidae

Diapriidae was formally included in the Proctotrupoidea with a number of other somewhat questionably related families that have all now been separated and placed in their own superfamilies. Having a single family in its own superfamily always looks strange, so it's worth pointing out that whilst Diapriidae is indeed the sole representative of Diaprioidea in Britain, there are actually five other families elsewhere in the world. The current British checklist recognises around 280 species in 37 genera, that are currently separated into three subfamilies; Belytinae, Diapriinae and Ismarinae. In older literature there were only two, Belytinae and Diapriinae, but two further families Ambositrinae and Ismarinae were accepted (Masner, 1976). The former is tropical, but the latter now includes the single genus Ismarus that was previously in the Belytinae. And, just to complicate matters further, it's now been proposed that Ismarinae should be elevated to family status.

Diapriids are tiny to small-sized (>7mm, but mostly 2-4mm), dark brown or black parasitoid wasps that typically occur in damp, shaded areas. Their antennal sockets are located low down on the front of the head not far above the clypeus, but not touching or directly above as in the Platygastroidea. On closer inspection it will be seen that they emerge from a frontal prominence or 'antennal shelf', which is a specific identifying feature of these species apart from the members of the rarely recorded Ismarus genus. Apart from the location of the antennae, the structure is also important in helping to identify the family, the sexes and the genera.

Although identification to species is unlikely from photos, it's certainly useful to understand how the 'keys' work, which in the case of Diapriidae starts with defining the family and the sex, as the males and females are treated separately. Apparently, it's relatively easy to determine the sex purely from the antennae. From what I can understand, in the Belytinae the females mostly have 15 segments (scape, pedicel and 13 flagellomeres), although there are a couple of exceptions that always puts a spanner in the works when trying to make a decision purely from a photo, and the males have 14; in the Diapriinae the females have either 12 (10 genera) or 13 (4 genera) that become slightly broader towards the tip, invariably forming a small club, the males have either 13 (4 genera) or 14 (10 genera) that, almost always, have modifications to the fourth segment (second flagellomere). In Belytinae, the modifications as they are known are on the first flagellomere. In all cases the scape is distinctly elongated, at least 2.5 times as long as wide.

Species and/or sexes of the same species may be apterous (lacking wings), brachypterous (reduced or short-winged) or fully-winged with reduced venation and no distinct pterostigma; forewings with at most three closed cells in Belytinae, or at most one, but usually none, in Diapriinae where the wings of some species are effectively veinless.  

In respect of their biology, members of the Belytinae are typically found in damp woodland or similar habitat where most species are believed to be endoparasitoids of Mycetophilidae and Sciaridae (Diptera) larvae. The Diapriinae on the other hand occur in a much wider range of habitat, with some species in places such as animal burrows or in the intertidal zone for example. Most are pupal endoparasitoids of higher Diptera. Many are gregarious and thirty of more could emerge from a single puparium. And some are associated with ants.

Despite the fact that some of these species are obviously widespread and probably quite abundant in certain areas or habitats, they are very poorly recorded by causal observers. Most of the records on the NBN Atlas are derived from specific datasets from just a few areas, and only a relatively small number of confirmed sightings over the past few years, so it's pretty much impossible to get an indication of the species that could be found locally. Admittedly, it would only be out of interest because, although I'm pretty sure that I would now be able to identify a diaphriid and hopefully sex it, I'm not sure I could go much further without help. Fortunately, there are some very knowledgeable individuals on the 'UK Bees, Wasps and Ants' FB group who are often able to provide assistance or at least make some tentative suggestions. And, there are some experts, which was the case here with the individual featured below, initially confirmed as a male diapriid, but with a comment that the identity couldn't be taken further without microscopic inspection. But, it was then looked at by one of the country's leading authorities from the NHM who confirmed that it was Basalys sp.

Unfortunately, I don't have a head on shot to show the location of the antennal sockets, but you can just about make out that they emerge low down from a facial prominence. The dorsal view shows various features including the wings with barely any visible venation and no stigma, the long antennal scape and, importantly, 12 flagellomeres with slight modification of the second (the fourth segment). From that information, I think that I could have confirmed it was a male from the Diapriinae subfamily. Knowing it was Basalys, I checked the 'key' and can now just about see the distinct basal vein, but there's absolutely no way that I could have confirmed the genus. Identification of males to actual species is extremely difficult even if you had the specimen to examine.

Although it's probably going to be a long while until I'm able to include a further example, I spent a fair amount of time researching and reading up about the family before writing this account. I always try to put the information I find into my own words. It takes time, but it's the way to learn.

New family added, March 25 (v.1)