With temperatures creeping up as the climate warms, those very hungry caterpillars could get even hungrier, and more abundant. Crop losses to pests may grow.
Insects will be “eating more of our lunch,” says Curtis Deutsch of the University of Washington in Seattle. Based on how heat revs up insect metabolism and reproduction, he and his colleagues estimate that each degree Celsius of warming temperatures means an extra 10 to 25 percent of damage to wheat, maize and rice. Their prediction appears in the Aug. 31 Science.
Insects already munch their way through 8 percent of the world’s maize and wheat each year, and damage 14 percent of rice, Deutsch says. If Earth’s average global temperature rises just 2 degrees above preindustrial levels, annual crop losses could reach about 10 percent for maize, 12 percent for wheat and 17 percent for rice. That’s a total loss of about 213 million tons for the three grains combined.
Unlike mammals and birds, insects heat up or chill as their environment does. As an insect warms, its metabolism speeds up, too. The faster it burns energy, the more ravenously the insect feeds and the sooner it reproduces. The speed-up rates aren’t hugely different across kinds of insects, Deutsch says. So he and his colleagues developed a mathematical simulation of how much insects as a whole would rev up, reproduce and ravage grains in warmer times.
Tropical insects are often already near the ceiling of their temperature tolerance, where an insect has to cope with so much heat damage that reproduction rates falter. In cooler temperate zones, where wheat is grown, insects have much more leeway to live faster. That makes future wheat especially vulnerable, Deutsch says.
This is “an incredibly valuable first step” toward predicting future pest losses, says physiological ecologist Nathan Lemoine of Colorado State University in Fort Collins, who studies plant–insect interactions. But he and others note that insect metabolism is just one factor out of many that will affect future crop yields for better or worse.
Farmers will likely adopt new defenses, though that would raise farmers’ costs, says Erich-Christian Oerke of the University of Bonn in Germany, who published data in 2006 that provided the starting point for the new study. Oerke was not involved in the new calculations.
Rising temperatures can encourage, or discourage, insects invading new territories. Temperatures may also affect the parasites that prey on crop-munching pests. Both pests and plants may adapt and evolve. Predictions will have to evolve, too.
“I don’t want people to think this is a sky-is-falling story,” Deutsch says. Hungrier insects will not wipe out these crops entirely. Yet any food loss can be consequential to people who have gotten hungrier themselves in a more crowded world.
Editor’s note: This story was updated on September 4, 2018, to correct the location of Colorado State University.