Stunning Fossils Show Ancient Parasitic Wasps Still Inside Their Unfortunate Hosts

By George Dvorsky on at

A meticulous examination of over 1,500 fly pupae fossils has resulted in the discovery of four new species of ancient parasitic wasps, dating back to between 66 million and 23 million years ago in what is now France.

New research published today in Nature Communications offers the first definitive proof of parasitic behaviour among wasps, or more accurately, the first definitive proof of endoparasitism among wasps, in which the parasite (like a wasp pupae or tapeworm) develops or lives inside its host. A team led by Thomas van de Kamp from the Karlsruhe Institute of Technology (KIT) used a powerful new scanning technique to peer inside the remains of 1,510 mineralised fly pupae, yielding 55 parasitic events. What’s more, the researchers were able to identify four previously unknown species of parasitic wasps and even conduct physical examinations of the new specimens, even though they’re trapped inside the mineralised fly pupae.

A small sampling of the 1,510 fossilised fly pupae used in the study. Image: Georg Oleschinski

Finding examples of parasitic behaviour in the fossil record is hard because it requires the parasite to be caught in the act of parasitising its host. What’s more, many parasites develop inside their hosts (as is the case here) and are not visible on the exterior of the fossil. Until now, the fossil record of parasitic wasps has been limited to isolated adults trapped in amber. But in this case, the researchers managed to discover fully developed wasps inside their fly hosts, which they did using a technique known as high-throughput synchrotron X-ray microtomography.

“We used a synchrotron — a type of particle accelerator—to generate intense X-rays in order to perform the high-throughput tomography scanning [cross-sections of solid bodies] of 1,510 samples in the scope of just one week,” van de Kamp told Gizmodo. “The study was performed by a highly interdisciplinary team of biologists, palaeontologists, physicists, computer scientists, and mathematicians. We employed a sophisticated experimental setup, built and run by physicists and computer scientists, algorithms for image analysis developed and optimised by mathematicians and relied on the expertise of palaeontologists and entomologists for the interpretation of our results. Seeing the scientists of the different disciplines working together closely and inspiring each other over the duration of the project has been an amazing experience.”

An X-ray projection of a fossil parasite, where the wasp is clearly visible inside the fly pupae. Image: Thomas van de Kamp

The fly pupae fossils were obtained from the Natural History Museum of Basel and the Swedish Museum of Natural History. The fly pupae and their parasitic contents date back to the Paleogene period, which began at the end of the Cretaceous period (so after the dinosaurs went extinct). The fossils from this collection were not dated by van der Kamp’s team, relying instead on earlier studies done on fossils found in the same region of France.

Of the 1,510 samples scanned, 55 yielded parasitization events, or about 3.6 per cent of the fossils. In almost all cases, the wasps were fully developed and on the cusp of departure. The fact that more premature wasps were not found suggests earlier stages, like eggs or larvae, weren’t prone to fossilisation, likely on account of their softer exoskeleton.

All of the wasps described in the new study developed as solitary parasites inside fly pupae. Their life cycle began with a female wasp laying an egg in a fly pupae. After hatching, the wasp larva fed on the still living fly pupa, ultimately causing its death. Once fully developed, the wasp emerged from its incubator, looking for a mating partner. After mating, the female wasps searched for fly pupa, re-starting the cycle.

A video showing the concealed parasitoid wasp inside a fossilised fly pupae.

Four new species of parasitic wasps were uncovered, all of which have now been endowed with the coolest names: Xenomorphia resurrecta, Xenomorphia handschini, Coptera anka, and Palaeortona quercyensis.

“The detail of preservation of many wasps was just exceptional,” said van der Kamp. “The 3D reconstructions of the tomographic data facilitated species descriptions as done for extant [living] species. We were also surprised how little is still known about the lifestyle of extant parasitic wasps, despite the huge number of species.”

Each species exhibited unique physical adaptations for the task of exploiting their hosts. Two of the species, X. resurrecta and X. handschini, are quite similar, which is why they were placed in the same genus, or family, of parasitic wasps. The main difference between these two species had to do with the shape of their waists.

Video showing how the tomography data was used to reconstruct the insect, in this case a female Xenomorphia resurrecta.

“The two other species, Coptera anka and Palaeortona quercyensis, differ from the Xenomorphia species by a number of exoskeletal expansions, serving as protections for articulation points,” said van der Kamp. “This may indicate a more ground-dwelling lifestyle. With its ‘horns’ and beak-like mandibles, Coptera anka is certainly the most peculiar-looking species described in the study.”

An important takeaway from this study is that old fossil collections, such as the ones used in this study, now deserve a second look. By using state-of-the-art imaging techniques, scientists can now acquire completely new insights from “forgotten” fossils. [Nature Communications]