Essential insects in East Asia have declined massively, study finds


Cabbage bugs, corn borers and other plant-eating insects important to ecosystems have declined dramatically in East Asia over the past two decades, according to a study published Friday in the journal Science Advances. has come

A team of scientists from the Chinese Academy of Agricultural Sciences in Beijing spent 18 years tracking the migration patterns of millions of insects belonging to nearly 100 species. The scientists weren’t just looking at how the abundance of a single type of bug changed over time. They also wanted to understand how a change for one affects others who are related to it through the food chain.

They found that overall levels of insects flying through an important migration corridor between China, the Korean Peninsula and Japan decreased by about 8 percent, and levels of predatory insects decreased by about 20 percent in summer. A decline in plant-eating insects led to a decline in predatory insects, reducing their ability to act as controls at the top of the food chain.

“Everything is connected,” said Chris Wikhuis, a visiting professor at the Chinese Academy of Agricultural Sciences and co-author of the study published in the US-based journal. “One species will begin to disappear or experience a dramatic decline in abundance, and those links in the food web will also begin to weaken — eventually the whole web will unravel.”

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Dragonflies, beetles and other predatory insects deter plant-eating insects. Without predators, plant eaters such as aphids and caterpillars are free to forage. The consequences can spread to humans when herbivores target crops such as corn, soybeans and cotton that people rely on for food and economic development.

Every year from 2003 to 2020, scientists tracked flying insects on Beihuang Island in Bohai Bay between China and the Korean Peninsula. Using radar and light traps that attract high-flying insects, they found that as insects eating the plants declined, so did the insects that ate them. Finally, the absence of predator species allows others to spread unchecked, with impacts on the food chain.

The research echoes other studies that have found similarly alarming rates of insect extinction, including butterflies on the American prairie, beetles in the forests of Puerto Rico and bees in German marshes.

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A reduction in pests does not appear to cause widespread problems. But insects play an important role in ecosystems by polluting plants and controlling pests that threaten essential crops. Some scientists worry that a large-scale big die-off could throw ecosystems around the world out of balance, cause food chains to unravel, and lead to the abundance of some species and the extinction of others. Is. Other scientists have debated whether the die-off is worldwide or limited to specific locations.

The team’s findings in Beijing highlight a fundamental principle of ecology: that an imbalance at one level of the food chain can wipe out all others.

“As climate changes in the future, food webs are going to change dramatically, depending on who wins and who loses,” said Matthew Moran, professor emeritus of biology at Hendricks College in Arkansas. Is.” Losing keystone species can have a bigger impact than the decline of relatively rare species, Moran said.

The iconic wolves in Yellowstone National Park are a symbol of how important predators are to biodiversity. In the 20th century, wolves were absent from the park for 70 years. Without its top predator, the ecosystem fell out of balance. Elk and deer overgrazed trees that were essential shelter for birds. In 1995, a pack of Canadian wolves was released into the park. A few years after wolves reintroduced, elk and deer declined, while trees and birds rebounded.

“The same thing happens in the insect world,” Wyckhuys said. “Predators like dragonflies and lady beetles, these are the wolves of the insect world.”

As the top levels of the food chain disappear, the lower levels—like aphids and caterpillars—overwork their food sources, throwing plants out of balance as well.

“These predators that sit at the top of the food web are very vulnerable to extinction,” said David Wagner, an ecologist at the University of Connecticut. “They need all the bottom pieces to survive. They are among the most vulnerable species on the planet.”

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According to environmentalists, there are many reasons why insects die. Roads, agriculture and invasive species encroach on their habitat, and pesticides pollute what’s left. Climate change has led to irregular weather and weather patterns.

“The new climate that humans are creating will benefit some insects and be detrimental to others,” Moran said.

Die-off may not be irreversible. Studies such as those conducted by scientists in Beijing that reveal food web relationships between predators and prey can help ecologists develop recovery plans that include measures such as reintroducing predator species. are

“When we implement recovery measures, we’re usually successful,” Wagner said. “We have the knowledge and the tools to change things.”

The research could also help scientists develop new pest control methods for food crops, reducing the need for pesticide use by deploying predatory insects instead. “Insects — they do something in the world,” Wyckhuys said. “They provide important services to humanity.”

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