Why are insects disappearing?

International study reveals more than 500 combined factors causing global decline in insect populations and suggests not just focusing on bees and butterflies

Insects are disappearing at an alarming rate around the world, and scientists are trying to understand why. While increased agricultural cultivation is often cited as the main cause, new research from Binghamton University in New York State reveals a much more complex picture, involving hundreds of factors combined.

Interest in reports of insect declines has rapidly increased since a groundbreaking 2017 study found a 75% decline in insect numbers in less than 30 years. These alarming findings have led to a wave of studies, each exploring potential causes.

To get a comprehensive picture of the scientific consensus, researchers at Benjamin Franklin University examined more than 175 scientific review articles. These reviews included more than 500 hypotheses about the drivers of insect population decline. From these, they built an integrated network of about 3,000 possible links, including everything from desertification to urban sprawl.

“It’s hard to talk to everyone and understand what everyone thinks. Instead of inviting 600 people into a room, we decided to read every review or meta-analysis article,” said Christopher Halsch, a postdoctoral researcher and lead author of the paper. “The idea is to extract the ‘causal pathways’ from the articles: for example, agriculture leads to pollution, which causes insect populations to decline. Then we built a huge network to see which ideas are uniquely connected and which pressures are seen as root causes.”

The extensive review shows that the most cited cause of insect decline is intensive agriculture, through land use change and the use of pesticides.

Missed Combined Threats

But the system is more complex than ranking individual drivers – factors interact and influence each other. For example, climate may be a driver of insect declines, but under the umbrella of climate there are specific factors such as extreme precipitation, fires and temperature, which shape additional pressures. It is a synergistic and interconnected network.

At the same time, many of the threats recognized in the IUCN report were barely mentioned in the literature on insect declines. “None of the articles mentioned natural disasters,” notes Prof. Eliza Grames, who led a study that showed a 20% decline in butterflies in the US. “We didn’t look at human impact, the effects of war or the construction of railways. There are broad areas that we know are threats to biodiversity, but the literature on insect declines focuses on a few prominent stressors, rather than getting into the more specific and mechanistic ones.”

Bias in research and focus on struggles

The researchers found biases in the recent literature, particularly a focus on “popular” and “charismatic” insects such as bees and butterflies, even though they are a small minority in insect diversity.

“Because we’ve invested so much in bees and butterflies, we’re limited in developing conservation actions that will benefit other insects,” Grimes added. “When you give funding to bee research, you learn more about bees,” added Halsch.

The researchers state that insect conservation will require management not only of individual factors, but a multi-pronged, systemic approach.

“Conservation actions that are overly biased towards certain insects or specific pressures can harm many other insects,” said Halsch. “If we focus only on bees and butterflies, we will miss a wide range of species, in fact the vast majority of them.”

for the scientific article

More of the topic in Hayadan:

• The silent collapse of the insect kingdom
• Insect resistance to pesticides
• Environment for insects and vice versa
• Switch to eating insects?
• Symbiosis between insects and microorganisms