Global warming means that insects will destroy more crops, say researchers from the University of Washington who led a study. There have already been warnings that climate change will probably impact our crops. More frequent extreme weather events like droughts and rising global temperatures will affect our ability to feed ourselves. This latest study warns about rising insect populations, insect activity, and declining crop yields.
Curtis Deutsch and colleagues wrote about their study and findings in the journal Science (citation below). Deutsch is Associate Professor of Chemical Oceanography at the University of Washington School of Oceanography.
More insects in temperate regions
The researchers said that that there will be more insects and insect activity in the world’s temperate regions. These regions are precisely where most of our crops are.
The increase in the number of insects will occur along with temperatures rises.
The authors forecast that more insect activity will boost global losses of corn, rice, and wheat. For every degree Celsius rise in Earth’s mean surface temperature, crops losses will increase by 10% to 25%, they say.
This means annual losses of about 213 million tons just in these three crops.
Regarding greater crop losses due to insect activity, Prof. Deutsch, co-lead author, said:
“We expect to see increasing crop losses due to insect activity for two basic reasons. 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.”
Infestations of insects and global warming
The United Nations estimated in 2016 that at least 815 million people globally didn’t have enough food to eat. Wheat, rice, and corn are staple crops for approximately four billion people.
These three crops also account for two-thirds of our food energy intake, says the UN Food and Agriculture Organization (FAO).
Co-author Rosamond Naylor said:
“Global warming impacts on pest infestations will aggravate the problems of food insecurity and environmental damages from agriculture worldwide.
“Increased pesticide applications, the use of GMOs, and agronomic practices such as crop rotations will help control losses from insects. But 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.”
Naylor is a professor in the Department of Earth System Science at Stanford University. She is also a founding director of the Center on Food Security and the Environment.
Insects and crops – the study
To determine how insect herbivory on crops might affect future food supplies, the researchers looked at decades of laboratory experiments on insect reproductive and metabolic rates. They also gathered and analyzed data from ecological studies of insects in the wild.
The body temperature of insects tracks the temperature of their environment. In other words, they are ectothermic. Humans and other mammals are not ectothermic.
Therefore, the temperature of the air affects insects’ caloric requirements, oxygen consumption, and other metabolic rates.
How temperature increases affect insects
The researchers saw that past experiments showed conclusively that rises in temperature would accelerate insect metabolism. A rise in insect metabolism subsequently boosted their appetites at a predictable rate.
Rising temperatures also boosted their reproductive rates up to a point. When temperatures reach what they are today in the tropics, reproductive rates level off.
The authors found that the effects of temperature on insect demographics and metabolism were consistent across different species. Temperature rises affected the metabolic and reproductive rates of, for example, aphids and corn borers.
Prof. Deutsch and colleagues folded these reproductive and metabolic effects into a model of insect population dynamics. They subsequently looked at how different climate change scenarios changed that model.
Regarding temperate regions, co-author Scott Merrill said:
“Temperate regions are currently cooler than what’s optimal for most insects. But if temperatures rise, these insect populations will grow faster.”
“They will also need to eat more because rising temperatures increase insect metabolism. Together, that’s not good for crops.”
Merrill is a researcher at the University of Vermont’s College of Agriculture and Life Sciences and the Gund Institute for Environment.
A 2°C global temperature rise
What would happen if there were a 2°C rise in global mean surface temperatures? Their model predicted that insects would destroy 31% of global corn crops. Rice and wheat yields would also decline – by 19% and 46% respectively.
The word ‘yield,’ in this context, refers to crop production per unit of area. It may also simply refer to total crop production.
Total annual corn crop losses would reach 62 million tons. Rice and wheat crop losses would reach 92, and 59 million tons respectively.
Unsurprisingly, rice regions would see smaller declines than wheat and corn regions. That is because rice grows mainly in the tropics while the other crops grow in temperate regions. Temperatures are already optimal for maximum insect metabolic and reproductive rates.
Therefore, any extra temperature rises affects insects less in the tropics than in the temperate regions.
The authors note that governments and farmers could shift where crops are grown. They could also try breeding insect-resistant crops. However, these alterations cost money. They also take time.
Prof. Deutsch said:
“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.”
Joshua Tewksbury, director of Future Earth at the University of Colorado, is a co-lead author. Other co-authors are David Battisti, a UW professor of atmospheric sciences, Raymond Huey, a UW professor emeritus of biology, and Michelle Tigchelaar, a UW research scientist in the Department of Atmospheric Sciences.
The Gordon and Betty Moore Foundation and the National Science Foundation funded the study.
“Increase in crop losses to insect pests in a warming climate,” Curtis A. Deutsch, Joshua J. Tewksbury, Michelle Tigchelaar, David S. Battisti, Scott C. Merrill, Raymond B. Huey, and Rosamond L. Naylor. Science, 31 Aug 2018: Vol. 361, Issue 6405, pp. 916-919. DOI: 10.1126/science.aat3466.