The wasps that killed the flies millions of years ago

Parasitic insects are vanishingly rare in the fossil record, which means that the evolution of parasitism as a survival strategy is unclear.

Until now, for instance, there has only ever been one example found of a parasitoid wasp inside a host fly pupa. It was found in the Quercy region of France and dates from about 40 million years ago.

Following publication of a report in the journal Nature Communications, however, the situation is substantially improved. Researchers led by Thomas van de Kamp from the Laboratory for Applications of Synchrotron Radiation in Karlsruhe, Germany, have added several more examples to the list.

Using high-throughput synchrotron X-ray microtomography, Van de Kamp and colleagues examined 1510 fossilised fly pupae, all deriving from France and dating to Paleogene period, between 66 and 23 million years ago.

All up, they found 55 of the flies were harbouring parasitic wasps, all previously unknown to science, when they died.

The researchers say all four species – dubbed Xenomorphia resurrecta, X. handschini, Coptera anka and Palaeortona quercyensis – were solitary insects.

They also note that parasitic wasps might have been much more common than the evidence suggests. Of the 55 wasps discovered, 52 were adults which presumably died just before emerging from the pupae. This implies that the fragile exoskeletons of younger specimens did not survive initial decomposition.

The finding, they conclude “highlights the need for closing the existing knowledge gap of the morphological and biological diversity of extant parasitoid wasps”.