Climate change drives expansion of invasive insects on West Coast

Climate change has led to warmer temperatures in the Pacific Northwest, leading some insect species to expand their ranges into oak savannas farther north, according to new research from Binghamton University, University of New York State.

Side by side, Dylan Jones posted photos of two oak leaves. One, healthy and green, dotted with occasional galls, a structure made by a herbivorous species of oak gall wasp. The other leaf was yellowed and tattered, the victim of a population of predatory insects without checks and balances. Climate change has caused warming temperatures in the Pacific Northwest, resulting in species such as Neurotereus saltatorius to extend their range into the oak savannahs further north.

“In the native range, you can find a handful of galls on a single leaf. In the expanded range, you sometimes find thousands on a single tree,” said Kirsten Prior, assistant professor of biological sciences. “It’s pretty prevalent all over Vancouver Island.”

Jones, a doctoral candidate in biological sciences at Binghamton University 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 of “The latitudinal gradient in species diversity offers elevated niche opportunities for an expanding phytophagous insect” include Prior, field technician Julia Kobelt, then undergraduate Jenna Ross and assistant professor of science biologics Thomas Powell.

Oak savannahs are grassy and shrubby areas where oaks are the dominant tree species. The species of oak in question — Quercus garryana — requires a dry environment. As a result, oak savannahs often lie in the rain shadow of the West Coast mountain range, Prior explained.

A diverse and ecologically important group of trees throughout North America, oaks are home to a wide variety of insect species, such as oak gall wasps. These wasp species form growths called galls that can be striking in their various shapes, from those that look like large apples to others with colorful spikes reminiscent of sea urchins.

Interestingly, Alfred Kinsey – yes, this Kinsey – studied oak gall wasps before shifting his field of study to human sexuality.

“Biologists and hobbyists have long fascinated this group of species because they are quite charismatic,” Prior said. “You can go into an oak tree and see all these structures on it.”

In addition to their herbivorous creators, these galls host other species of insects, including a dazzling variety of parasitoid wasps, one of the most diverse and ecologically important groups in the animal kingdom, the latter for their role in insect control. harmful. Parasitoid wasps lay their eggs in the gall; after hatching, their larvae then eat the oak gall wasp larvae.

Oak gall wasps are highly diverse in North America, but are 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 to document biodiversity. We still haven’t described much of the biodiversity on Earth, especially with insects,” Prior said.

Ecosystem invaders

The researchers checked their study sites three times during that summer. Some were quite remote, involving travel on dirt logging roads, or located on Bureau of Land Management property or on reservations associated with Indigenous communities. Others were suburban, located a short distance from cities.

Due to urbanization, few oak savannahs remain on Vancouver Island; those that remain are well documented and maintained by the landowners.

“We’ve had long relationships with many landowners there who 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 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 with no diversity of predators and competitors, ultimately overwhelming the ecosystem.

The case of oak gall wasps highlights the importance of biodiversity and the potential long-term ramifications of climate change, the researchers point out.

“Biodiversity can be very 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.”