Hidden Parasitic Wasps Discovered Spreading Across the U.S.

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In the intriguing realm of biodiversity, a groundbreaking discovery is raising eyebrows and piquing curiosity among scientists and nature enthusiasts alike. A dedicated research team from Binghamton University, part of the State University of New York, has unveiled not one but two previously unknown species of parasitic wasps, known scientifically as Bootanomyia dorsalis, which have made their way to North America from Europe. This revelation not only enriches our understanding of ecological diversity but underscores the intricate dynamics of species interaction within our environment.

Though these tiny wasps may not boast the vibrant allure of butterflies, they are most certainly gaining traction in the field of ecological research. Measuring a mere 1 to 8 millimetres in length, these diminutive insects are responsible for creating the distinctive tumour-like growths on oak trees known as “galls.” These galls can range in size from a pinhead to an apple, taking on various shapes that can resemble sea urchins or saucers. Kirsten Prior, Associate Professor of Biological Sciences at Binghamton University, who also co-leads the Natural Global Environmental Change Center at the university, explains that these wasps serve as a fascinating emblem of biodiversity.

North America is home to around 90 different species of oak trees and approximately 800 species of oak gall wasps that thrive on them. The parasitic wasps play a critical role in this delicate ecosystem by laying their eggs within the galls, subsequently consuming the oak gall wasps that reside there. This prompts an essential question: just how many species of parasitoid wasps exist across the landscape? It’s a query that has captured the attention of both academic researchers and everyday nature enthusiasts.

The recent article featured in the Journal of Hymenoptera Research, titled “Discovery of two Palearctic Bootanomyia Girault (Hymenoptera, Megastigmidae) parasitic wasp species introduced to North America,” sheds light on a previously uncharted dimension of species diversity. The research team, which includes not only Professor Prior but also current graduate student Kathy Fridrich and former graduate student Dylan G. Jones, alongside collaborators from the University of Iowa and the Stone Barns Center for Food and Agriculture, has embarked on an extensive journey to deepen our understanding of these fascinating organisms.

This significant discovery forms part of a broader research initiative. In 2024, the National Science Foundation awarded a substantial grant of $305,209 to Binghamton University to delve into the diversity of oak gall wasps and their parasitoids across North America. This project represents a collaboration among esteemed experts, including Prior, Andrew Forbes from the University of Iowa, Glen Hood from Wayne State University, and Adam Kranz, a pioneer behind Gallformers.org, a website dedicated to educating the public about identifying galls on North American plants.

The NSF grant tackles a pivotal question: How do gall-forming insects evade the myriad of evolving parasitic wasps, and conversely, how do these parasites adapt to catch up? To unravel this mystery, researchers are gathering oak gall wasps from across North America and employing cutting-edge genetic sequencing techniques to identify which parasitic wasps emerge from the galls. Among the dedicated researchers are Fridrich and fellow Binghamton graduate student Zachary Prete, who spent an enlightening summer embarking on a collection expedition from New York to Florida.

“Our research focuses on how the characteristics of oak galls serve as defensive mechanisms against parasites and influence the evolutionary pathways of both oak gall wasps and their parasitic counterparts,” Prior elaborated. “This study is set to be the most comprehensive cophylogenetic investigation of its kind. Only through a concerted effort to explore biodiversity can we unveil surprises, such as the existence of new or introduced species.”

Unveiling the Unknown Species

In recent years, researchers affiliated with Prior’s lab have traversed the West Coast, from California to British Columbia, meticulously collecting around 25 species of oak gall wasps and rearing tens of thousands of parasitic wasps, ultimately identifying over 100 distinct species. Among these parasitoids, some were revealed to be the European species Bootanomyia dorsalis, belonging to the wasp family Megastigmidae. Researchers at the University of Iowa identified a similar wasp within their collections made in New York state.

“Discovering this potential European species on both coasts of North America prompted our research group to confirm the identity of this parasitic species and ascertain whether it was indeed an introduced species from Europe,” said Prior.

Identifying parasitic wasps can be a challenging endeavour due to their small size and subtle features. To overcome this hurdle, researchers employ genetic tools to validate species identities, sequencing the “universal barcoding gene,” Cytochrome Oxidase Subunit I (mtCOI), and comparing their findings against established reference libraries. Their results revealed that the European species B. dorsalis exists in two distinct varieties, or clades: the samples from New York were related to populations in Portugal, Iran, and Italy, while those from the Pacific coast had links to species from Spain, Hungary, and Iran.

“The genetic sequences from the two clades were sufficiently different that they can be classified as separate species. This indicates that B. dorsalis was introduced to North America on at least two occasions, suggesting that the introductions to New York and the West Coast were separate events,” Prior explained.

Interestingly, while the B. dorsalis wasps found on the West Coast were genetically identical, indicating a small, localised introduction, the East Coast wasps exhibited slightly greater genetic diversity. This could suggest a less severe population bottleneck or that the species was introduced multiple times.

But how did these European species make their way to North America? One possibility is the intentional introduction of non-native oak species. The English oak, or Quercus robur, was extensively planted for timber since the 17th century and can be found in British Columbia as well as several northeastern states. Additionally, the Turkey oak, Q. cerris, is an ornamental tree now flourishing along the East Coast, including areas close to where B. dorsalis was identified in New York.

There are other potential scenarios. Adult parasitic wasps can live for up to 27 days, which opens up the possibility of them having inadvertently “hitched a ride” on an aircraft, as Prior suggested.

Researchers are still assessing whether these introduced species pose a threat to native North American populations. Past introductions of parasitic species have been known to impact native insect populations adversely, which raises valid concerns.

“Our findings indicate that these wasps can parasitise multiple oak gall wasp species and have the potential to spread,” Prior noted. “Given that the West Coast population likely expanded across regions and host species from a small introduction, they could be influencing the populations of native oak gall wasp species or other indigenous parasites.”

Role of Naturalists and Citizen Scientists

Naturalists and citizen scientists play a pivotal role in biodiversity research, as evidenced by the project that led to the identification of the two clades of B. dorsalis. Gall Week, a project hosted on the platform iNaturalist, actively encourages citizen scientists to collect galls during two seasons. Specimens gathered during the NSF-funded study will be featured on the naturalist site Gallformers.org, further enhancing public engagement in ecological research. Binghamton University’s ecology classes have also participated in Gall Week and contributed to the university’s annual Ecoblitz biodiversity event.

Biodiversity is a key pillar of healthy ecosystems, and it is increasingly threatened by the forces of global change. “Parasitic wasps are arguably the most diverse group of animals on Earth and play a crucial role in ecological systems, acting as biological control agents to regulate insect populations, including those that threaten crops and forests,” Prior emphasised.

As we delve deeper into the intricate tapestry of life around us, discoveries like that of the Bootanomyia dorsalis wasps remind us of the importance of preserving biodiversity and understanding the complex relationships that underpin our ecosystems. The work of researchers, combined with the enthusiasm and contributions of citizen scientists, is vital in ensuring that we continue to uncover the hidden treasures of our natural world, fostering a healthier planet for generations to come.

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