Rare Parasitic Wasps from Europe Found in the US for the First Time

Newsweek

15 hours ago

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Scientists have just identified two previously unknown species of parasitic wasps living in the United States.
The discovery is described in a study in the Journal of Hymenoptera Research led by biologist professor Kristen Prior of Binghamton University.
Her research is part of a larger initiative that explores the diversity of oak gall wasps and their defense against their parasitic predators.
Prior explains in the study that while they are only about 1–8 millimeters long, oak gall wasp are known for creating the tumor-like plant growths known as "galls."
These growths can be small as a pinhead or large as an apple, and take on different shapes, with some resembling sea urchins, others saucers, and so on.
A stock image shows a parasitic wasp on a green leaf.
A stock image shows a parasitic wasp on a green leaf.
getty images
North America has around 90 different species of oak trees, and around 800 species of oak gall wasps that live upon them. Then there are parasitic wasps, which lay their eggs in the galls and go on to devour the entire oak gall wasp.
The newly discovered species belong to the family of Bootanomyia Girault, which live in the palearctic region of northern Europe and Asia.
Their presence in America is unexpected, suggesting the possibility of other such species still waiting to be discovered.
This study is supported by the National Science Foundation, which in 2024 awarded a $305,209 grant to Binghamton University for research into the diversity of oak gall wasps and parasitoids throughout North America.
To uncover these hidden species, researchers went on a summer expedition from New York all the way down to Florida, collecting galls and analyzing the parasitic wasps that emerged, using genetic sequencing to identify them.
"We are interested in how oak gall characteristics act as defenses against parasites and affect the evolutionary trajectories of both oak gall wasps and the parasites they host", Prior said.
The scale of the study makes it the most extensive of its kind, she added. "Only when we have a large, concerted effort to search for biodiversity can we uncover surprises—like new or introduced species."
Over the past several years, researchers led by Prior also traveled the West Coast from California to British Columbia, collecting approximately 25 oak gall wasp species, identifying more than 100 different species.
Some of the parasitoids turned out to be Bootanomyia dorsalis from Europe. They were also found in New York by University of Iowa researchers.
Upon further analysis, they discovered that while the East Coast wasps were likely to have come from Portugal, Iran and Italy, the ones from the West Coast were likely to have originated in Spain, Hungary, and Iran.
This suggests at least two separate introductions of the species into this country. Moreover, East Coast wasps showed more diversity.
Researchers believe their introduction may have been facilitated by the planting of non-native oaks like Quercus robur and Q. cerris, or even by accidental transportation via airplane.
"Parasitic wasps are likely the most diverse group of animals on the planet and are extremely important in ecological systems, acting as biological control agents to keep insects in check, including those that are crop or forest pests," Prior said.
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Reference
Brown, G. E., Lewis, C. J., Fridrich, K., Jones, D. G., Goodwin, E. A., Weinrich, C. L., Steffensen, M. J., Prior, K. M., & Forbes, A. A. (2025). Discovery of two Palearctic Bootanomyia Girault (Hymenoptera, Megastigmidae) parasitic wasp species introduced to North America. Journal of Hymenoptera Research, 98, 653–665. https://doi.org/10.3897/jhr.98.152867