Diapriidae

HYMENOPTERA > APOCRITA | Parasitica > Diaprioidea > Diapriidae

Formally included in the Proctotrupoidea, the Diapriidae family, together with the closely associated Ismaridae, are now taxonomically placed within the superfamily Diaprioidea along with three other related families that do not occur in the UK.

There is no up to date, publicly available, British Checklist for this particular family, but a bit of research suggests that there are now close on 300 recognised species in 37 genera, which are separated into subfamilies Belytinae and Diapriinae.

Two additional subfamilies were introduced (Masner, 1976): Ambositrinae, a southern hemisphere group, and Ismarinae established for the single monotypic genus Isamarus, which in older literature was included within the Belytinae. With the reclassification of the Diaprioidea, the subfamily was elevated to family status, Ismaridae. Six species are listed, although only three are recorded. They are rare and are not likely to be found accidently and, given that they are now treated as a separate family, are not included here.

Diapriids are tiny (>6mm, but mostly 2-4mm), dark brown or black parasitoid wasps that typically occur in shady areas. The primary identifying feature of the family is that the antennal sockets are located low on the front of the forehead, not far above the clypeus, emerging from a frontal prominence or ledge, commonly referred to as an antennal shelf.

Although in most cases identification to species is unlikely from photos it should be possible to determine the subfamily and sex purely from the form and structure of the antennae. Females and males are treated separately and, for any chance of determining the genus, identification always starts with the antennae. 

In the Belytinae subfamily the females typically have 15-segmented antennae (scape, pedicel and 13 flagellomeres), very rarely 14; the exception is Synacra which only has 12, but species from that genus are seldom recorded; the males always have 14 with the third segment (a3, or first flagellomere) modified.

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 (a4, or second flagellomere). In all cases the scape is distinctly elongated, at least 2.5 times as long as wide.

Different species, 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; in the Belytinae the forewings have relatively complete venation, usually with three closed cells, whereas in the Diapriinae the forewings either have reduced venation or, in some species, appear almost 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 wider range of habitats including the coast where a few species actually live on the beach in the intertidal zone, whilst others are associated with animal burrows and ant nests. The adults don't tend to fly very much as they spend most of the time on the ground on or in soil and litter in search of host pupae.

Despite the fact that many diapriids are 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, with 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.

I ended the previous version of this family account with a comment that it would probably be a fair while before I would be able to include further examples, but I'm pleased that I can now represent four more genera, so I'm now extending the account onto a second page.

Updated, May 26 (v.2)