Invasion of super insects

Heone day, about 60 million years ago, a tiny leafcutter moth landed on an ancient sycamore tree to lay eggs on its leaves. The larvae grow up and make a nest in a convenient hook, which looks like a sleeping bag, made between thin layers of leaves. After hatching, they came to the surface and went to immortalize their relatives. Most of the chewed leaves fell to the ground and rotted shortly afterwards.

But this leaf, along with a few lucky others, deserved something else, an unimaginable feat approaching immortality. When it fell, this leaf either sank into the mud or was carried away by the flood river, which buried it in layers of sediment. There, it survived and fossilized for millennia, away from oxygen and bacteria that would have finished what the larvae did. One day, the scientist who discovered such fossils, Lauren Azevedo-Schmidt, lay there in the dark until she saw it in a fossil bed in southern Wyoming.

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Azevedo-Schmidt removed the leaf from the rock with a paleo stick and cut it from a stone slab. In his lab at the University of Wyoming, where he was working on his doctoral dissertation, he put the fossilized leaf under a microscope and examined the remnants of prehistoric larval handiwork and noted the damage—round pockets that look like holes. where creatures live. He then added the sample to the existing collection of chewed and scratched ancient leaves, which by the end of his doctoral work had become a veritable forest: 77,763 samples.

Within this “stone forest,” Azevedo-Schmidt and her supervisor, paleoecologist Ellen D. Currano, documented different types of leaf damage—a concept they describe as “damage diversity.” They found seven types of miniature decimation, ranging from holes to piercings. They then compared the damage done by prehistoric insects to the damage caused by modern creatures. The results flew in the face of their expectations.

They found that compared to beetles from the late Cretaceous period – about 67 million years ago – modern beetles cause unprecedented amounts of damage to plants. The most recent leaves from modern forests and existing herbaria—the Smithsonian Environmental Research Center in Maryland, Harvard Forest in Petersham, Massachusetts, and Le Salva in Costa Rica—are more chewed, punctured, and misshapen than centuries ago. .

Compared to prehistoric leaves, modern leaves also tend to break down in more ways. They also had a higher “damage frequency” – meaning that recent specimens had more chewed and misshapen leaves than older ones. This pattern intensified in the last century, suggesting that the industrial revolution played a role.

“The difference in insect damage between the modern era and the fossil record is striking,” says Azevedo-Schmidt, now a postdoctoral researcher at the University of Maine. They also found that the level of damage has increased rapidly over the past century. Herbarium specimens from the early 2000s were 23 percent more likely to be damaged by insects than those from the early 1900s.

GOOD AND GONE: Mother Nature often offers creative solutions when population dynamics are disrupted, such as a predatory fungus that liquefies gypsy moth larvae (above) in bumper years. But time will tell if our intervention has tipped the balance too far in favor of the insects. Photo by Pedro Luna/Shutterstock.

This stark difference in herbivore levels was particularly strange to observe given recent concerns about declining insect populations, the researchers said.1 and fears of an apocalypse of insect death.2 “Despite the widespread distribution of insects, it was surprising to find such unprecedented damage,” says Azevedo-Schmidt.

Their findings were published in October this year Proceedings of the National Academy of Sciencesadd a terrifying new twist to the ecological fate of plants and trees.3 Today, more than ever, we need forests to capture carbon and convert carbon dioxide into oxygen to combat climate change. But people are destroying forests to make room for animal feedlots. Lumber companies run chainsaws around the clock to supply wood for houses, furniture, guitars, paper. Trees like the mighty Dutch elm are being decimated by disease pandemics. And now comes the possibility of breeding swarms of super-insects that are crossing paths in the forests of our age.

“Like all good research, it led to a lot of other questions,” says Ryda Krell, who studies insect-plant interactions at Western Connecticut State University. If the team found that insects were destroying plants at a similar rate in the past, it would mean that because forests survived in the past, insects are less likely to knock them down now, he says. “But instead we find ourselves in a very uncertain place.”

Azevedo-Schmidt and her colleagues don’t have definitive answers about how we got here, but they offer several theories based on the complex interplay of climate change, invasive species, evolution, pollutants and selective pressures.

Perhaps, for example, there is a force linking climate change to more voracious insects. Indeed, scientists associate warming temperatures with an increase in insect crop losses.4 Currano says that when looking at the rock record, that dynamic doesn’t tell the full picture. The Paleocene period, when many specimens were collected, was so warm that palm trees and alligators lived in what is now Wyoming. What’s more, temperatures and carbon dioxide levels rose many times during the time the fossil leaves were sampled, but leaves from that time were significantly more intact. “So if insect damage is controlled only by increasing temperature and increasing CO2, we should have seen spikes in herbivores,” says Azevedo-Schmidt. “But we didn’t see that.” This means that some other factor makes today’s insects more predatory.

Are we looking at a dark, leafless future?

Another possibility is a more recent rapid scale movement of insect species. After the industrial revolution, people began to travel more than ever before – first by boats and trains, then by cars and planes. They began to transport and distribute plants, animals, and insects to new locations, sometimes accidentally, but many times intentionally, facilitating the spread of invasive species that destroyed native plants, often on a larger scale than the insects that coexisted with them. centuries ago.

The evolutionary dynamic between plants and their eaters also favors the latter. Trees grow slowly, while insects grow faster. Trees take decades to grow, and some can be centuries old, so they are not particularly flexible when it comes to change. But insects, which typically have short lifespans, are more adaptable to environmental changes such as temperature or a new food source. In this race for survival, “plants just can’t keep up,” Azevedo-Schmidt says, leaving them open to increased predation, especially if something changes in their environment.

Finally, we can download errors even more directly. We kill the weak with the pesticides, insecticides and other toxic chemicals we use to kill unwanted creatures that destroy our crops or annoy us. Survivors are super creatures with super appetites. It’s a phenomenon similar to the superbugs of the microbial world—the more antibiotics we use, the tougher and more resistant microbes we breed. “Pesticides make me very angry because they create selective pressure and create very, very predatory insects,” says Azevedo-Schmidt. While we don’t know if or how pesticides affect the insects’ hunger, the survivors may have a voracious appetite, the researchers say. And these insects do not stop at the periphery of agriculture. They often eat in forests.

Does this mean we’re looking at a bleak, leafless future? Now more than ever, we need our trees – to capture carbon and convert carbon dioxide into oxygen to fight climate change. Scientists say they are somewhat optimistic that we can still fix things by fairly obvious means, such as avoiding chemical use.

But Azevedo-Schmidt hopes that we too can get backup from Mother Nature, which sometimes kicks in unexpected, eleventh-hour self-regulatory mechanisms.

He gives an example. Gypsy moth larvae brought to the Americas in the 1800s with the idea of ​​using them for silk production (Lymantria dispar) can defoliate large areas of forest in years of multiple hatching. But then a different biological force comes along, in this case a predatory fungus, essentially liquefying the exterminating bugs. “It turns the caterpillars into this green ooze that drips from the trees and spreads everywhere,” says Azevedo-Schmidt. “So there’s kind of a system of checks and balances,” he said, so forests can still grow in our future.

For his part, Krell has some faith in human ingenuity to help clean up the messes we’ve made. “As a population, we are so innovative by nature,” he says, that we can still save our forests from the increasingly insatiable insects. “We don’t give up, which I think is why we’re so successful as a species. That’s why I remain hopeful.”

Lina Zeldovich grew up in a family of Russian scientists, listening to bedtime stories about volcanoes, black holes and brave explorers. wrote for The New York Times, Scientific American, Reader’s Digestand Audubon Magazine, among other publications, and has won four awards for its coverage of poop science. His book, Other Dark Matter: The Science and Business of Turning Waste into Wealth, published in 2021 by the University of Chicago Press. You can find it at LinaZeldovich.com and @LinaZeldovic.

Lead image: Iamjohnhult / Shutterstock

References

1. Outhwaite, CL, McCann, P., & Newbold, T. Agriculture and climate change are reshaping insect biodiversity worldwide. Nature 60597-102 (2022).

2. Goulson, D. The insect apocalypse: “Our world will stop without them.” Guardian (2021).

3. Azevedo-Smith, L., Meineke, EK, & Currano, ED Insect herbivores are more abundant within modern forests than in remnant sites. Proceedings of the National Academy of Sciences 119e2202852119 (2022).

4. Deutsch, CA, and b. Increased yield loss to insect pests in a warm climate. Science 361916-919 (2018).




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