A collage of oak galls created by oak wasps. Credit: Kirsten Prior
Climate change has led to warming temperatures in the Pacific Northwest, prompting some insect species to expand their range into oak savannas further north, according to new research from Binghamton University , State University of New York.
Side by side, Dylan Jones showed photos of two oak leaves. One was healthy and green, dotted with something else, a structure made by a herbivorous species of oak wasp. The other leaf was yellowed and torn, the victim of a population of predatory insects without checks and balances. Climate change has led to warming temperatures in the Pacific Northwest, which has led species such as Neurotereus saltatorius to expand their range into oak savannas further north.
“In the native range, you might find a handful of galls on a single leaf. In the expanded range, you’ll sometimes find thousands on a single tree,” said Assistant Professor of Biological Sciences Kirsten Prior. “That’s pretty common on Vancouver Island.”
Jones, a PhD candidate in biological sciences at Binghamton University and a Clifford D. Clark Diversity Fellow, is the lead author of a research paper recently published in Journal of Animal Ecology about the situation Co-authors on “Latitudinal gradient in species diversity provides elevated niche opportunities for an expanding phytophagous insect” include Prior, field technician Julia Kobelt, then-student Jenna Ross and assistant professor of Science Biological Thomas Powell.
Oak savannas are grassy and shrubby areas with oaks as the dominant tree species. The oak species in question — Quercus garryana — requires a dry environment. As a result, oak savannas are often in the rain shadow of the West Coast Range, Prior explained.
A diverse and ecologically important group of trees throughout North America, oaks are home to a wide variety of insect species, including oak wasps. These species of wasps form growths known as galls that can be surprising in their varied shapes, from those that resemble large apples to others with colorful spikes reminiscent of sea urchins.
Interestingly, Alfred Kinsey—yes, that Kinsey—studied oak wasps before transitioning his field of study to human sexuality.
“There has been a long fascination by biologists and hobbyists with this group of species because they are quite charismatic,” Prior said. “You can go to an oak tree and see all these structures.”
In addition to their herbivorous creators, these galls host other species of insects, including a dazzling array of parasitoid wasps, one of the most diverse and ecologically important groups in the animal kingdom, the latter for their role in controlling insect pests. Parasitoid wasps lay their eggs in the gall; after hatching, their larvae eat the oak wasp larvae.
Oak wasps are very diverse in North America, but not well documented; their evolutionary relationships and even the identification of some species remain unknown. A consortium of scientists across the continent is working to change that; Jones and Prior are part of that effort.
“It’s important to continue documenting biodiversity. We still haven’t described a lot of Earth’s biodiversity, especially with insects,” Prior said.
Invaders of ecosystems
The researchers checked their study sites on three separate occasions over the course of that summer. Some were quite remote, involving travel over logging roads or were on Bureau of Land Management property or reserves associated with indigenous communities. Others were suburban, located a short distance from cities.
Due to urbanization, there are few oak savannas left on Vancouver Island; those that remain are well documented and cared for by the landowners.
“We’ve had longstanding relationships with a lot of property owners there that allow us to work on their property,” Prior said. “Some of them are so excited to have researchers there.”
Biodiversity tends to work on a latitudinal gradient, Jones added: The closer you are to the equator, the more species you have. A similar situation is true when it comes to higher altitudes. When a species can expand its range due to warming temperatures, it can move into areas without a diversity of predators and competitors, ultimately overwhelming the ecosystem.
The case of oak wasps highlights the importance of biodiversity and the possible long-term ramifications of climate change, the researchers point out.
“Biodiversity can be really important in potentially protecting areas from invasive species,” Jones said. “If we have strong competitors and predators, that could make areas less susceptible to invasive species.”
The crypt guard wasp has been found to parasitize several species of gall wasp. More information: The latitudinal gradient in species diversity offers great niche opportunities for an expanding phytophagous insect. Journal of Animal Ecology (2022). DOI: 10.1111/1365-2656.13780 Provided by Binghamton University
Citation: Climate change leads to spread of invasive insects on US West Coast (2022, August 10) Retrieved August 10, 2022, from
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