Insects are disappearing at an alarming rate worldwide, but why? Agricultural intensification tops the list of proposed reasons, but there are many other, interconnected drivers that have an impact, according to new research led by Binghamton University, State University of New York.
Research on insect decline has surged in recent years, sparked by an alarming 2017 study that suggested that insect populations had declined by 75% in less than three decades. This has led to countless published papers, with scientists hypothesizing different reasons for the decline.
To better understand the scientific community's views more broadly, a team of researchers at Binghamton University analyzed more than 175 scientific reviews, which included 500+ hypotheses on different drivers of insect decline. Using this information, they created an interconnected network of 3,000 possible links, including everything from beekeeping to urban sprawl.
"It's really hard to talk to everybody about what everyone thinks. And so instead of getting 600 people into a room, we decided to take an approach where we read every paper that's either a review or a meta-analysis," said Christopher Halsch, a post-doctoral researcher at Binghamton and lead author of the paper. "The idea was to read them and extract what people say are 'causal pathways'. For example, agriculture leads to pollution, which leads to insect population decline. Then we built a giant network out of them to see which ideas are more often connected to each other, and which stressors are most often seen as the root causes."
Examining the massive list of possible links, the most cited driver for insect decline was found to be agricultural intensification, via issues like land-use change and insecticides.
But it's more complicated than ranking drivers, as systems are interconnected and impact one another. For example, climate might be a driver for insect decline, but there are individual drivers under the umbrella of climate, like extreme precipitation, fire and temperature, which themselves can impact other drivers. It's a highly connected and synergistic network.
And still, many ideas are overlooked. The International Union for the Conservation of Nature , for example, has a list of all the potential threats to consider in insect conservation. But huge portions of that list never made an appearance in recent insect decline literature.
"None of the papers mentioned natural disasters," said Assistant Professor of Biological Sciences Eliza Grames , who was part of a recent study showing a 20% loss of butterflies in the U.S. "No papers looked at human intrusions and disturbance, or the effects of war on insects, or railroads. So there are these big areas that we know in general are threats to biodiversity, but the insect decline literature is really just focused on a few big stressors, as opposed to getting into the more specific ones, which are a lot more mechanistic."
The researchers identified biases in recent literature, most notably those generated from a focus on "popular" and "charismatic" insects like bees and butterflies, despite them being in the vast minority of insect biodiversity.
"Because people have focused so much on pollinators like bees and butterflies, we are limited in identifying conservation actions that benefit other insects," said Grames.
"Bees are agriculturally important and people care about them. So there is a lot of research priority towards funding research on bees," added Halsch. "So you get this kind of feedback: if you prioritize research on bees, you learn more about bees."
The researchers noted that insect conservation will require managing not just individual drivers but addressing systems from a multi-pronged approach.
"One of the important points we're trying to make in the paper is that conservation actions overly biased towards certain insects or certain stressors will likely be negative for many other insects," said Halsch. "If we focus too much on bees and butterflies and their conservation, we will miss a lot of other species, most of them in fact."
The study, "Metasynthesis reveals interconnections among apparent drivers of insect biodiversity loss," will be published in BioScience on April 22.
