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Climate change leads to invasive insect expansion on the US West Coast

A collage of oak galls made by oak gall wasps. Credit: Kirsten Prior

According to new research from Binghamton University, State University of New York, climate change has led to rising temperatures in the Pacific Northwest, causing some insect species to expand their range into more northern oak savannas.

Side by side Dylan Jones showed pictures of two oak leaves. One was healthy and green, dotted with the occasional gall, a structure made by a herbivorous species of oak gall wasp. The other leaf was yellowed and torn, the victim of an insect population with no predatory checks and balances. Climate change has led to rising temperatures in the Pacific Northwest, causing species such as Neurotereus saltatorius to expand their range into more northern oak savannas.

“In the native range, you might find a handful of galls on a single leaf. In the extended range, you can sometimes find thousands on a single tree,” said assistant professor of Biological Sciences Kirsten Prior. “This is quite common on Vancouver Island.”

Jones, a Binghamton University doctoral student in biological sciences and Clifford D. Clark Diversity Fellow, is the lead author of a research paper recently published in the Journal of Animal Ecology on the situation. Co-authors on “Latitudinal gradient in species diversity offers great niche opportunities for a range-extending phytophagous insect” include Prior, field technician Julia Kobelt, then-undergraduate Jenna Ross, and assistant professor of biological sciences Thomas Powell.

Oak savannas are grassy and shrubby areas with oak as the dominant tree species. The oak species in question – Quercus garryana – needs a dry environment. As a result, oak savannas are often found in the rain shadow of the west coast mountain range, Prior explained.

Oaks, a diverse and ecologically important group of trees throughout North America, are home to a wide diversity of insect species, such as oak gall wasps. These wasp species form growths known as galls that can be striking in their various shapes, from those that resemble large apples to others with colorful spines reminiscent of sea urchins.

Interestingly, Alfred Kinsey — yes, that Kinsey — studied oak gall wasps before crossing his field into human sexuality.

“There has been a long-standing fascination of biologists and amateurs with this group of species because they are quite charismatic,” Prior said. “You can go up to an oak tree and see all those structures on it.”

In addition to their herbivorous creators, these galls harbor other insect species, including a dazzling variety of parasitic wasps, one of the most diverse and ecologically important groups in the animal kingdom, the latter for their role in controlling insect pests. Parasitic wasps lay their eggs in the gall; after hatching, their larvae eat the larvae of the oak gall wasp.

Oak gall 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 this effort.

“It’s important to continue to document biodiversity. We still haven’t described much of Earth’s biodiversity, especially with insects,” Prior said.

Ecosystem invaders

Over the course of that summer, the researchers checked their study areas on three separate occasions. Some were quite remote, with treks on dirt roads, or on Bureau of Land Management properties or on reservations associated with Indigenous communities. Others were suburbs, a short distance from cities.

Due to urbanization, few oak savannas remain on Vancouver Island; the ones that remain are highly documented and maintained by landowners.

“We have had long relationships with many landowners that allow us to work on their property,” Prior said. “Some of them are so excited to have researchers there.”

Biodiversity tends to operate on a latitude gradient, Jones added: The closer you are to the equator, the more species you have. A similar situation applies 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 the oak gall wasps highlights the importance of biodiversity and the possible long-term consequences of climate change, the researchers emphasize.

“Biodiversity can be very important in potentially protecting areas from invading species,” Jones said. “If we have strong competitors and predators, this can make areas less susceptible to invading species.”

Crypt-keeper wasp found to parasitize multiple gall wasp species

More information:
Latitudinal gradient in species diversity offers great niche opportunities for a range-extending phytophage insect, Journal of Animal Ecology (2022). DOI: 10.1111/1365-2656.13780

Provided by Binghamton University

Quote: Climate Change Leads to Invasive Insect Expansion on the US West Coast (2022, Aug. 10) retrieved Aug. 10, 2022 from https://phys.org/news/2022-08-climate-invasive-insect-expansion-west.html

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