Dirhinus, Quadrhinus group (Chalcididae: Dirhininae), an oxymoronic wonder.
As an advocate for popularising the insect diversity of Kenya (we have Elephant, Loxodonta africana, and Lion, Panthera leo, why not celebrate the majesty of thousands of insect species). Until recently the reasons were twofold, small size of the subject, and inadequate photographic technology. Innovative development in both hardware (e.g. Canon’s great MP-E 65 mm lens) and automontage software (e.g. Zerene stacker) solved both problems. Today it is not uncommon to render tack-sharp high-resolution images of the smallest creatures, in our case insects. As a result, taxonomists, in describing new species, can more readily view characters that distinguish among the smallest of insects. The rest of us can marvel at the complexity of these most important animals. Nature has a great imagination.
The insect of this week is one that is close to me. Dirhinus (di = two; rhinus = horns) is a genus in the family Chalcididae that was described and named by the Swedish Zoologist Johan Wilhelm Dalman (1787-1828). With its horns, Dirhinus was so obviously different from other Chalcididae that it deserved its own subfamily (Dirhininae), for which Dirhinus is the type genus. The genus numbers about 70 species worldwide, all of which are pupal parasitoids of Diptera (flies). Dirhinus females attack the host fly, on or slightly under the ground, injecting a single egg into the defenseless fly host as the latter completes its larval stages and begins to pupate. The wasp, probably using its two shovel-like horns, digs into the soil burying the host slightly under the ground. The Dirhinus egg hatches and consumes the fly pupa. The newly emerged adult wasp probably uses its horns to dig out to the surface. Among the fly hosts of Dirhinus wasps are Tephritidae (true fruit flies, e.g. Ceratitis capitata) several of which are important pests of edible fruits, and Tsetse flies (Glossina species), so this wasp genus is truly human friendly.
Now to the surprise. In October of 2016 I noticed, in one of our collections, a strange wasp, resembling a small Dirhinus but with 4, not 2 horns (see image). This was an exciting discovery and I immediately sent images of the wasp to two experts in the family, both of whom thought that this was a developmental anomaly and most probably a genetic “monster”. However, over the next couple of years I collected several new specimens of the 4-horned variety from 7 different collection sites in semi-arid habitats. Clearly the original specimen was not a freak. These specimens were sent out for study by the aforementioned expert whose thorough examination revealed not one, but rather 5 separate species. The five species have now been described. Except for the obvious difference in the number of horns there wasn’t enough to create a new genus for the group. Together they became Dirhinus, subgroup Quadrhinus), the oxymoronic 4-horned 2-horned wasp, a Kenyan endemic.
A short note. The family name for the Chalcididae is derived from the name of the first genus to be placed (described) in the family. That genus was Chalcis which was described by the great Danish taxonomist Fabricius (Johan Christian Fabricius, 1745-1808). Fabricius was a student of Linnaeus and described an astronomical 9776 species. There is a large town named Chalcis on the Greek island of Euboea. Perhaps the 1st specimen was collected in or near that town. I found nothing further related to the etymology of Chalcis.
Credits: Dr Robert Copeland