By simulating these changes across the globe, the team calculated that the most productive agricultural regions will also be the most severely affected, with France, China, and the United States suffering the brunt of the incipient wave of pests. But the consequences of a global decline in grain will likely have the biggest effects on the poorest nations and households—those that are already living on a nutritional knife-edge.
Many factors, for which there is little data, could complicate and change the team’s estimates. For example, “the team don’t seem to have considered the influence of warming on the predators of these pests,” says Navin Ramankutty, who studies food security at the University of British Columbia. Along with hunters like spiders, every insect is targeted by at least one species of body-snatching parasitic wasp, which helps to keep their numbers in check. “If they also respond positively to warming, that might somewhat mute the impact of the crop pests themselves,” Ramankutty says.
Many pest insects also rely on bacterial symbionts that help them to digest their meals or provide them with essential nutrients. There’s a smattering of evidence that some of these microbes are very sensitive to high temperatures, which might again limit their hosts’ ability to thrive in the heat. And of course, extreme weather, from heat waves to droughts, might kill insect pests directly.
Finally, insects can obviously move. Besides changing their behavior to avoid the hottest part of the day, over time, entire populations could also move to new locations, tracking temperate climates northward as many animals are already known to do. These changes could have unknown consequences for the overlaps between pests and crops.
American trees are moving west, and no one knows why.
These intricacies might change the degree of the losses that Deutsch predicts, but it’s hard to imagine that they might wipe away those losses entirely. This, he says, is the time to start preparing, whether through agricultural practices like crop rotations, or by applying pesticides, or by planting genetically modified crops. “But preventing climate change is the thing I would first turn to,” he adds.
“Humanity faces this food-security challenge at a time when training and job opportunities for expert entomologists are shrinking,” writes Markus Riegler from Western Sydney University in an accompanying editorial. “These experts are urgently needed” to deal not just with the problem of pests, but also with threats to insect biodiversity.
Most of the millions of species of insects are not pests. They are the linchpins of many ecosystems. They’re sources of food for birds, and carriers of pollen for plants. If insects decline, ecosystems everywhere will too. And insects are declining, even in protected areas worldwide. As I wrote in The Atlantic last year, “Insects are the most diverse and numerous group of animals on the planet. If they’re in trouble, we’re all in trouble.”