Rising global temperatures mean pests will devour far more of the world’s crops, according to the first global analysis of the subject, even if climate change is restricted to the international target of 2C.

Increasing heat boosts both the number and appetite of insects, and researchers project they will destroy almost 50% more wheat than they do today with a 2C rise, and 30% more maize. Rice, the third key staple, is less affected as it is grown in the tropics, which are already near the optimal temperature for insects – although bugs will still eat 20% more.

Rising heat stress on crops is already expected to cut cereal yields by about 10% for 2C of warming, but the new research indicates rising pest damage will cause at least another 4-8% to be lost. With 800 million people chronically hungry today and the global population rising towards 10bn, increasing pest destruction will worsen food security.

“For many, many people in the world there is already a shortage of food, so it is not like we can afford to spare [more],” said Prof Curtis Deutsch at the University of Washington, US, who led the work. “A lot of people in the world, the most vulnerable, can’t afford to give up anything.”

The losses are likely to be underestimates as the scientists did not consider factors such as increased transmission of crop diseases carried by insects, or losses after harvest when the grain is stored. The research also did not assess the risk of population explosions of insects that can wipe out crops, due to the complexity of such events.

The research, published in the journal Science, started with well-established knowledge about how rising temperature affects insects. “Warmer temperatures increase insect metabolic rates exponentially [and] increase the reproductive rates,” said Deutsch. “You have more insects, and they’re eating more.” The team then added data on today’s pest losses and used a range of climate change models to estimate future losses – all showed significant damage.

Overall, losses were found to increase by 20-50% for 2C of warming above pre-industrial levels and 40%-100% for 4C. The latter will be reached this century if carbon emissions are not cut soon. “The overall picture is, if you’re growing a lot of food in a temperate region, you’re going to be hit hardest,” said Scott Merrill at the University of Vermont, another member of the team.

Europe’s breadbasket is among the hardest hit, with 11 nations predicted to see a rise in pest losses of 75% or more. “France will get a double whammy,” said Merrill, as it is a top five producer of both wheat and maize. Another big wheat producer, Russia, will see losses rise from 10% to 16% with 2C of warming. Across the globe, an extra 200m tonnes of grain are expected to be eaten by insects in a 2C warmer world.

Wheat ear flowering aphids on wheat plant.

The research was deliberately conservative and so did not allow population explosions of pests to take place in the computer simulations, as it’s difficult to model how these develop, but such explosions cannot be ruled out.

Deutsch noted that warmer winters have led the pine bark beetle to kill off forests across North America: “They just come out gangbusters in the spring. You can see the damage to space.”

“It is an example of what can happen when you have huge tracts of land that are essentially single crops species with one major pest,” he said. “That is similar in many respects to what agriculture has produced – miles and miles of a single plant.” He also said insect population explosions are seen in fossils from warming periods in the Earth’s past.

Markus Riegler, at Western Sydney University in Australia and not part of the research team, said the new work was the first global analysis. “The results show that insects will cause significantly increased grain loss across many regions of a warmer world,” he said. The work used data on 38 insect species but Riegler said the results should be verified for more pests in future.

“The substantial increases in pest damage forecast call for action on climate change [emissions] and adaptation,” he said. “Everyone must be involved in change: farmers, industries, policymakers and wider society.”

Sources: https://www.theguardian.com/environment/2018/aug/30/crop-losses-to-pests-will-soar-as-climate-warms-study-warns