Insects could eat twice as much wheat by the end of the century

Climate change can lead to larger populations of hungry insects. This can have serious consequences for grain-growing regions in the northwest and around the world.

"And of course the effects of these insects will come on top of the impact of climate change," says Curtis Deutsch, an earth scientist at the University of Washington. The paper, which Deutsch wrote with an interdisciplinary team of scientists, was published on Thursday in the journal Science.

The researchers looked at the top three cereals in the world: wheat, corn and rice. On the basis of their model, the temperature of every 2 degrees Celsius increased, the amount of crops consumed by insects would increase considerably: by 19 percent for rice, 31 percent for corn and by 46 percent for wheat.

So if the Earth warms up by 4 degrees Celsius – which, according to scientists, is on track to do at the end of the century – wheat losses by insects would double.

To make that number easier to understand, Deutsch says it is useful to think of wheat losses by insects in terms of bread. For example, insects currently consume an amount of grain that corresponds to about one of the 12 loaves of bread, worldwide. If climate change continues unabated, they can consume two of every twelve loaves.

There are two important factors that underlie this change.

Insects burn more calories the warmer it is. That means they eat more, says Deutsch. "That is a very simple and well-known effect that in principle will be true for every crop and every insect that eats it."

But that is not all: if the temperature rises, warmer air also means more animals, to some extent. In really warm areas such as the tropics, insects can take off. But in the cooler, temperate regions where grains are grown, the populations can increase dramatically.

The researchers looked at 38 well-studied insects around the world. By estimating how much more the insects would eat in certain regions and combining these estimates with their predicted population changes, they could calculate how much grain could be lost.

For every degree that heats the earth, insects could consume 25% more wheat than they already do. By the end of the century, insect losses could double. The red parts of the map show where the loss of wheat by insects is expected to increase.

Wheat is an important product in Oregon and the Pacific Northwest, and Oregon and Washington were both among the top 10 wheat producing states in 2017. Per Portland port, wheat is Oregon's largest export by weight.

Deutsch says that according to their models, the northwest has the right conditions to see a large increase in insect-related loss.

"Our calculations would suggest that even with a few degrees of warming, the amount that the insects can consume can easily double," says Deutsch, although he notices that their model becomes less accurate as you look smaller at the area you are viewing.

Farmers can possibly fight the hungry insects by rotating crops, introducing biological controls (such as even hungry birds of prey) or increasing their use of pesticides.

Sanford Eigenbrode, an entomologist at the University of Idaho, says the study is one of the most robust and comprehensive solutions to climate change and insect-related crop loss, although plant-to-plant interactions in real life are more complex than any model could to be.

And changes in temperature and carbon dioxide (CO2) emissions can also be harmful to the wheat depending on the situation. Earlier this year, fires that were possibly reinforced by climate change destroyed much of Oregon's wheat cultivation. A few studies have shown that the excess of CO2, which plants use for photosynthesis, could in the first instance stimulate the types of wheat in the northwest. But many others have discovered that climate change will lead to a worldwide decline in wheat, maize and rice yields – even before insects are taken into account.

The picture is not all bad. Heat waves in Montana lead scientists to test new, drought-resistant varieties of wheat, but it remains to be seen if they will be successful. Moreover, these models assume that the carbon emission rates will continue at their current speed. "It will only heat as much as we allow it," Deustch notes.

Copyright 2018 Oregon Public Broadcasting

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