At the current rate, nearly half of all insect species could be extinct within the next several decades—and pesticides play a major role, according to a new scientific report.

Among other factors, researchers found declines linked to the overuse of synthetic pesticides, many of which have only been on the market for the past 20 years.

“We are certainly losing fertility in the soils planted with insecticide-treated seeds, as these chemicals sterilize the soil of bugs, grubs, and anything else that recycles organic matter,” said Francisco Sanchez-Bayo, an ecologist at the University of Sydney in Australia, and lead author of the study.

The report, published in Biological Conservation, marked the most comprehensive longitudinal study to date, incorporating data from 73 historical surveys of insect populations from across the globe.

Forty-one percent of insect species are on the decline, of which 30 percent are endangered already, Sanchez-Bayo told Bloomberg Environment.

In addition to threats from pesticides specifically, the report also singled out impacts from changes in land use and climate change.

Growing Body of Evidence

Before this study tied global trends together, research on insect populations in Germany, Puerto Rico, and the U.K., found as much as 70 percent of the insect biomass in those countries may already be gone—a red flag for conservation groups.

“Everything we do is tied to insects,” said Scott Hoffman Black, director of The Xerces Society for Invertebrate Conservation, an Oregon-based nonprofit.

Black points to a 2006 study that said insects provide as much as worth $57 billion in economic value in the U.S. alone. The take-home message, Black said, is that declining populations are caused by humans and will have real impacts going forward.

“If you like to eat salmon, you can thank a fly that that salmon fed on when it was little, before it got out to the ocean,” he said. “If you like to eat fruit that is healthy and tasty, thank a pollinator.”

Pesticides Role

Many agricultural organizations point to practices such as integrated pest management programs designed to minimize insect exposure to chemicals, particularly to pollinators.

Black also claims that many of the newer classes of systemic pesticides sold today, such as neonicotinoids, are more devastating for insects.

“Very few are highly targeted,” he said.

“Neonics are incredibly long-lived in plants and soil, in some cases they’re still around years after the application and they also move across landscapes.”

CropLife, a trade group representing pesticide makers, didn’t respond to a request for comment.

However, in a 2018 publication from Bayer AG, Christian Maus, Bayer’s global lead scientist for bee care, cautioned that causes for insect declines were being influenced by subjective perceptions “that are gaining more and more weight through constant repetition and retelling like a snowball that rolls down the mountain,” he wrote.

While Maus agreed that significant drops in flying insects were recorded in Germany over the last 30 years, he cautioned that the conclusions environmental groups drew about the cause were often not based in science.

“Naturally, their theory was that conventional agriculture in general and chemical crop protection in particular were behind it all,” he said. “Such reflex accusations are, of course, ideologically motivated and have nothing to do with fact-based arguments.”

Need for More Study?

Many scientists agree that this new report marshals some of the best evidence to date of widespread insect population declines, but others say more research is necessary to draw firm conclusions.

“Scientists need to be cautious, a lot of initial studies turn out to not reflect reality,” said Bob Peterson, a professor of entomology at Montana State University and president of the Entomological Society of America.

While he isn’t advocating a wait-and-see approach, Peterson said more data collection is still necessary to determine what historically “normal” insect population numbers are.

“Back in the 1950s, ‘60s and ‘70s, when we had these relatively high population numbers, we were also rather indiscriminately spraying lots and lots of insecticides,” he said.

Moreover, Peterson said, policy makers should be cautious about putting too much blame for insect declines on pesticides only.

“If you taking more and more acres to grow corn, or build suburbs, you are radically reshaping the landscape and creating less diversity of plants. I would say that that overwhelms any impacts from pesticides,” said Peterson.