November 15, 2018

Crop-eating insects flourish as global temps rise

Rice, maize, wheat yields threatened, UVM research shows

Crop losses for critical food grains will increase substantially with global warming, as rising temperatures boost the metabolism and population growth of insect pests, according to new research from the University of Vermont.

“Climate change will have a negative impact on crops,” said UVM faculty member Scott Merrill, a co-author of the research study published in the magazine Science. “We are going to see increased pest pressure from climate change.”

The research team looked at how the insect pests that attack three staple crops — rice, maize and wheat — would respond under a variety of climate scenarios. They found that rising global temperatures would lead to an increase in crop losses from insects, especially in temperate regions. Losses are projected to rise by 10-25 percent per degree of warming.

A two-degree rise in global average temperature will result in total crop losses of approximately 213 million tons for the three grains, the researchers say.

The losses will come from an increase in insect metabolism, and from faster insect population growth rates. The link with metabolism is straightforward: “When the temperature increases, the insects’ metabolism increases so they have to eat more,” said Merrill, a researcher in UVM’s Department of Plant and Soil Science and Gund Institute for Environment. “That’s not good for crops.”

The link with insect population growth, however, is more complex. Insects have an optimal temperature where their population grows best. If the temperature is too cold or too hot, the population will grow more slowly. That is why the losses will be greatest in temperate regions, but less severe in the tropics.

“Temperate regions are not at that optimal temperature, so if the temperature increases there, populations will grow faster,” said Merrill, an ecologist who studies plant-crop interactions. “But insects in the tropics are already close to their optimal temperature, so the populations will actually grow slower. It’s just too hot for them.”

According to the study, wheat, which is typically grown in cool climates, will suffer the most, as increased temperatures will lead to greater insect metabolism as well as increased pest populations and survival rates over the winter. Maize, which is grown in some areas where population rates will increase and others where they will decline, will face a more uneven future.

In rice, which is mostly grown in warm tropical environments, crop losses will actually stabilize as temperatures rise, as population growth drops, counteracting the effect of increased metabolism in the pests.

That means that the most substantial yield declines will happen in some of the world’s most productive agricultural regions.

“The overall picture is, if you’re growing a lot of food in a temperate region, you’re going to be hit hardest,” said Merrill.

“I hope our results demonstrate the importance of collecting more data on how pests will impact crop losses in a warming world — because collectively, our choice now is not whether or not we will allow warming to occur, but how much warming we’re willing to tolerate,” said Curtis Deutsch of the University of Washington, who co-led the study with Joshua Tewksbury, director of Future Earth at the University of Colorado, Boulder.

Reduced yields in these three staple crops are a particular concern, because so many people around the world rely on them. Together they account for 42 percent of direct calories consumed by humans worldwide. Increased crop losses will result in a rise in food insecurity, especially in those parts of the world where it is already rife, and could lead to conflict, researchers say.

As farmers adapt to a changing climate by shifting planting dates or switching to new cultivars, they will also have to find ways to deal with pests, by introducing new crop rotations, or using more pesticides. But not all of these strategies will be available to all farmers.

“There are a lot of things richer countries can do to reduce the effect, by increasing pesticide use or expanding integrated pest management strategies,” said Merrill. “But poorer countries that rely on these crops as staple grains will have a harder time.”

The research was funded by the National Science Foundation and the Gordon and Betty Moore Foundation.

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