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Hotter weather leads to decline of some winged insects, study finds

A black fly sits on a green leaf.
Tony Hisgett
A fly sits on a leaf under a lilac tree in a backyard in the Quinton, England, on Oct. 8, 2009. Researchers believe climate change is putting stress on some winged insects, leading to their decline.

Researchers from the Rocky Mountain Biological Laboratory recently found that some winged insects native to the Mountain West – and crucial to maintaining ecosystem balance – are on the decline.

The study, published in the journalEcosphere in August, reports that the abundance of flies, wasps and moths dropped by more than 60% from 1986 to 2020.

The decline in insects is not new to the science world – it’s been noted in many previous studies globally. But most of those studies are in agricultural settings, so it can be hard to tell if variables like pesticides or human interference were the main culprits.

The nonprofit Rocky Mountain lab’s research, on the other hand, was conducted in a meadow surrounded by forests and protected from development. With those factors controlled, researchers like Brian Inouye believe the proof is in the pudding: climate change is putting stress on insects.

Brian Inouye sits on a rocky outcropping with rocky mountain peaks in the background.
N. Underwood
Brian Inouye, a professor of biological science at Florida State University and a corresponding author on the study, sits on a mountain near Crested Butte in Colorado in July.

“If we've got a hot, dry summer or a winter without much snow, then the following year tends to be a lower insect population,” he said.

The lab has collected and counted insects for over 34 years – one of the longest insect studies in North America. The late Michael Soulé began amassing a wealth of data on insects and passed it onto Inouye’s father, David Inouye. He recently retired, and his son continued collecting data for the last six years.

The motive when Soulé started was pure curiosity.

“We weren't thinking about the effects of climate change on insect populations,” Inouye said. “That just wasn't part of the public or scientific concern at that time.”

A small tent with clear netting sits in a green meadow with a gray rocky mountain in the background.
Brian Inouye
One of the Rocky Mountain Biological Laboratory's Malaise traps sits on a hill near Gothic Mountain in the background in June 2023. The insect trap was named after an entomologist who noticed that flies and moths tend to fly to the top of a tent as they are drawn to the light. The trap today has a collection jar so researchers can collect and count the insects.

The researchers collected the insects using a Malaise trap. The trap was named after René Malaise, an entomologist who noticed that flies and moths tend to fly to the top of a tent as they are drawn to the light. The trap today has a collection jar at the top where insects can fly in and out. But during the study period, the researchers closed the top for two days of the week so that Inouye and others could bring trap specimens back to the lab and sort out what was caught.

“We sort them into the major orders of flies, wasps, moths,” he said. “Then we dry them and we weigh them so that we know how many grams of insect food would be available for a bird in those couple of days.”

Researchers plan to add butterfly data to the study in the near future.

While some people are not fond of insects, the species provide food to many kinds of birds and even pollinate surrounding plants. Without insects, there could be a ripple effect throughout the ecosystem.

“There are fly species that are pollinators, it's not just our bees and butterflies that are important for keeping our wildflower populations so beautiful,” Inouye said.

He added that it’s hard to tell how insects are doing in the parts of the Mountain West that are drier than the wet meadow since it is a completely different environment than the one he studied. They may have learned how to adapt over time, or they could be much more sensitive to climatic changes. The latter is concerning to him.

“If our samples from this meadow are truly representative of what's happening at a broader landscape scale, then it's really worrying,” he said.

To save some of these insects in the community, Inouye suggests people use fewer pesticides and be mindful of outdoor lighting, which can expose certain insects to predators.

This story was produced by the Mountain West News Bureau, a collaboration between Wyoming Public Media, Nevada Public Radio, Boise State Public Radio in Idaho, KUNR in Nevada, KUNC in Colorado and KANW in New Mexico, with support from affiliate stations across the region. Funding for the Mountain West News Bureau is provided in part by the Corporation for Public Broadcasting.

I'm the General Assignment Reporter and Back-Up Host for KUNC, here to keep you up-to-date on news in Northern Colorado — whether I'm out in the field or sitting in the host chair. From city climate policies, to businesses closing, to the creativity of Indigenous people, I'll research what is happening in your backyard and share those stories with you as you go about your day.

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