Discovery of dinosaur-era wasp fossil from amber in Kuji City, Iwate Prefecture

A research group led by Professor Ren Hirayama of the Faculty of International Research and Education at Waseda University, Assistant Professor Nozomu Oyama of the Faculty of Dinosaur Paleontology at Fukui Prefectural University, and Associate Professor Mugino Kubo of the Graduate School of Frontier Sciences at the University of Tokyo, in collaboration with the Kuji Amber Museum (Director: Hisao Shinden), announced on July 10 that they have discovered fossilized wasps, possibly a new species of Proctotrupidae, in amber excavated from approximately 90-million-year-old Late Cretaceous strata adjacent to the museum. Two pieces of amber were discovered, one of which contains six individual wasps of the same species, a rare condition that may be related to their ecology. The results were presented at the 2025 Annual Meeting of the Palaeontological Society of Japan held at Hokkaido University at the end of June.

To date, more than 3,000 vertebrate fossils of 30 species have been discovered from these strata in Kuji City, Iwate Prefecture, including dinosaur teeth fossils and skeletal fossils of turtles and crocodilians.

The Kuji Amber Museum is an amber museum operated by Kuji Kohaku Co., Ltd. In Kuji City, Japan's largest amber production area, these fossils and amber are found in the Tamagawa Formation of the Kuji Group from the Late Cretaceous period, approximately 90 million years ago.

The wasps discovered are embedded in amber containing one individual (KMA00039) and amber containing six individuals (KMA00126). They were excavated near the museum and discovered in 2017 during amber processing work at the Kuji Kohaku factory. All seven individuals appear to have characteristics of the same species, with body lengths of approximately 4 millimeters, and some individuals are included in nearly complete condition with almost no damage.

Since the interior of amber cannot be observed without polishing, sample processing was carried out with the cooperation of the company's technicians. Subsequently, high-resolution observation and imaging were performed on the specimens embedded in amber using a confocal laser microscope at the University of Tokyo.

As a result, the insect fossils embedded in the two pieces of amber were found to be proctotrupid wasps. When researchers focused on the wing portions, all seven individuals were discovered to share common features: the pterostigma and Rs vein and r-rs vein of the forewing are developed forming an R cell (loop-like structure), while other wing veins show a tendency toward reduction. One individual contained in KMA00039 has a confirmed ovipositor and is considered to be female.

Based on these characteristics, the wasps embedded in amber closely resemble the subfamily Proctotrupinae, which includes the majority of the family Proctotrupidae in the superfamily Proctotrupoidea of parasitic Hymenoptera, and are considered to belong to this subfamily. There have been no previous discoveries of proctotrupid wasps from the same period in Japan. They have different characteristics from wasps found in relatively similar-aged Late Cretaceous strata in Lebanon and wasps belonging to the same subfamily from Myanmar. Regarding their fine structures, some areas are hidden by bubbles within the amber, so observation is currently continuing using X-ray CT at SPring-8 to remove them. More detailed structures are expected to be revealed in the future, and whether this is a new species will be confirmed upon publication of the paper.

The extremely rare point of note is that KMA00126 contains six individuals. Hymenoptera are broadly divided into phytophagous sawflies, social aculeate wasps, and parasitoid wasps. Modern proctotrupid wasps are parasitic, do not build nests, and act solitarily.

Future research will investigate the possibility that multiple proctotrupid wasps in the amber were parasitizing a single host, as well as the formation and embedding processes of the multiple pieces of amber.

Oyama commented: "In addition to the proctotrupid wasps discovered this time, diverse insects have been found from Kuji amber. I think that by conducting more detailed research on these insects in the future, we can connect this to understanding the ecology and evolution of insects that lived at that time. Kuji amber is temporally rare in the world and Kuji is likely a key locality for understanding the overall evolution of insects. I believe that by establishing preservation and research methods, we can expect further results."