In a paper published Aug. 31 in the journal Science, a team led by scientists at the University of Washington reports that the number of insects in today’s temperate, crop-growing regions will rise along with temperatures.
Researchers project that this activity, in turn, will boost worldwide losses of rice, corn and wheat by 10-25% for each degree Celsius that global mean surface temperatures rise.
Just a 2-degree Celsius rise in surface temperatures will push the total losses of these three crops each year to approximately 213 million tons, they say.
“We expect to see increasing crop losses due to insect activity for two basic reasons,” said co-lead and corresponding author Curtis Deutsch, a UW associate professor of oceanography.
“First, warmer temperatures increase insect metabolic rates exponentially. Second, with the exception of the tropics, warmer temperatures will increase the reproductive rates of insects. You have more insects, and they’re eating more.”
Co-author Rosamond Naylor, a professor in the Department of Earth System Science at Stanford University, said that increased pesticide applications, the use of GMOs, and agronomic practices such as crop rotations will help control losses from insects.
But she it still appears that “under virtually all climate change scenarios, pest populations will be the winners, particularly in highly productive temperate regions, causing real food prices to rise and food-insecure families to suffer.”
To investigate how insect herbivory on crops might affect our future, the team looked at decades of laboratory experiments of insect metabolic and reproductive rates, as well as ecological studies of insects in the wild.
Unlike mammals, insects are ectothermic, which means that their body temperature tracks the temperature of their environment. Thus, the air temperature affects oxygen consumption, caloric requirements and other metabolic rates.
The past experiments that the team studied show conclusively that increases in temperature will accelerate insect metabolism, which boosts their appetites, at a predictable rate.
In addition, increasing temperatures boost reproductive rates up to a point, and then those rates level off at temperature levels akin to what exist today in the tropics.
Deutsch and his colleagues found that the effects of temperature on insect metabolism and demographics were fairly consistent across insect species, including pest species such as aphids and corn borers.
They folded these metabolic and reproductive effects into a model of insect population dynamics, and looked at how that model changed based on different climate change scenarios.
Those scenarios incorporated information based on where corn, rice and wheat — the three largest staple crops in the world — are currently grown.
“Temperate regions are currently cooler than what’s optimal for most insects. But if temperatures rise, these insect populations will grow faster,” said co-author Scott Merrill, a researcher at the University of Vermont’s College of Agriculture and Life Sciences and the Gund Institute for Environment.
“They will also need to eat more, because rising temperatures increase insect metabolism. Together, that’s not good for crops.”