Climate change to accelerate crop losses from insects

By Joan Conrow

August 30, 2018

Climate change is expected to sharply reduce yields of three staple food crops as insect pests become hungrier and more numerous with warmer temperatures, a new study suggests.

Rice, maize and wheat, which comprise 42 percent of total human calorie consumption worldwide, will be greatly impacted by the intensified insect pest pressure projected with a 2-degree Celsius rise in global temperatures, according to a study published in the journal Science.

The warmer temperatures will deliver a double whammy by helping insect populations to thrive and also accelerating insect pests’ metabolic rate, prompting them to consume more food during their lifespan.

As a result, the study projects a 50 to 100 percent increase in pest-induced crop losses in European wheat, and 30 to 40 percent increases in losses of North American maize (corn). Eleven European countries are predicted to see 75 percent or higher increases in insect-induced wheat losses, including the UK, Denmark, Sweden and Ireland.

That translates into insect-induced losses of above 16 million tons annually in Europe’s bread basket — currently the most productive wheat producing region in the world. Similarly, farmers in the US, who grow most of the world’s maize crop, are projected to experience losses of more than 20 million tons annually. And China, which grows one-third of the global rice crop, could suffer insect-induced losses topping 27 million tons annually.

To help reduce losses, the study recommends several changes in the way agriculture is practiced globally, including breeding heat- and pest-resistant crops and adopting new crop rotation patterns. But greater pesticide use may also be needed in some instances to protect food supplies — despite the associated risks to environmental and human health.

“Fundamentally, climate change, and its effects on insects, speeds up the clock and puts more pressure on farmers, researchers and the rest of society to come up with sustainable solutions to a whole range of wicked problems that come together around the future of food,” said study co-author Joshua Tewksbury, who is also a research professor at University of Colorado, Boulder. “We have large and growing food needs, we are attempting to meet those needs without expanding agriculture into the last bastions of biodiversity and we are trying to do this without the massive problems that come from pesticide overuse.”

Adding to the challenge is our continued reliance on a small number of crop species, a fundamental lack of basic natural history knowledge about the plant species we depend on for food and the widespread practice of crop monocultures, he said. Though monocultures are efficient to farm, they are also very easy for insects to eat and provide excellent incubators for insect populations to grow rapidly and evolve quickly, reducing the effectiveness of many of control mechanisms, including pesticides.

“All of this produces a very fragile food system, and increased pest pressure simply increases the need for us to do the basic natural history needed to understand the systems in which our crops evolved,” Tewksbury said.

“Biological control of insect pests is successful when we have exceptional knowledge of the natural history of our crops and their relatives — where they grew, what insects ate the crops in the native range, what killed those insects. There is a lot of work to do to build that knowledge, and because our model is general — not specific to the three crops studied — we have reason to do this for all of our agricultural crops. That knowledge is out there to be gathered, and our inattention to this knowledge is perhaps the biggest threat to our food security.”

The researchers came up with their projection by calculating the potential for crop damage through 2050 by combining robust climate projection data, crop yield statistics, insect metabolic rates and other demographic information.

“On average, the impacts of insects add up to about a 2.5 percent reduction in crop yield for every degree C increase in temperature – for context, this is about half the estimated direct impact of temperature change on crop yields, but in north temperate areas, the impact of increases insect damage will likely be greater than the direct impact of climate on crop yields,” Tewksbury said.

Though pest populations may decline in some tropical areas as conditions get even hotter, they are expected to increase in more temperate regions as temperatures warm, creating a more conducive environment for insects.

The impacts are expected even if countries meet their existing commitments to reduce greenhouse gas emissions under the Paris Agreement. “Our baseline crop and climate data was set essentially at 1980-2000 values, and many of our tables and summary projections look at 2 degrees warming globally from that point,” he said.  “When we will reach 2 degrees warming depends on emissions.  At current rates of warming, we are very likely to reach 2 degrees warming from that baseline by 2050.”

The research builds on a paper that Tewksbury and co-author Curtis A. Deutsch published in the journal PNAS in 2008. It focused on the impacts of climate change on biodiversity, using the same principles employed in the new study.

“What we found was that many tropical animals, including insects, have fairly narrow tolerances to changes in temperature, while similar animals in the temperate zones have broader tolerances to changes in temperature because they have to in order to survive in a seasonal climate,” Tewksbury explained.

“In addition, the physiological optimum temperatures for tropical animals, including insects, was quite close to the actual temperature, while the optimum temperature for many animals in the temperate zones is much higher than the temperatures they often experience. As a result, warming tends to be a problem for tropical insects, but it benefits temperate insects. In this [new] paper, we took those same results, added a model of temperature effects on metabolism, and asked, what does this basic finding say about agricultural crop losses?”

The other authors of “Insect metabolic and population growth rates predict increasing crop losses in a warming climate” are Michelle Tigchelaar, David S. Battisti, Scott Merrill, Raymond B. Huey and Rosamond L. Naylor.