Many agricultural pests are benefiting from climate change.
armers around the world are spraying more chemicals than ever on their crops as they battle insect pests. Many of these small, hungry creatures have benefited from climate change, which has expanded their range, extended their breeding season, and made them harder to control with pesticides.
“As temperatures rise, managing pest attacks is becoming increasingly difficult as many of these pests multiply much faster,” said Laxman Mane, 50, who farms a plot of just under two acres in western India’s Haroli village, growing cauliflower, cabbage, cucumbers, okra, sugarcane and tomatoes.
“Earlier, none of these pesticides were required, but now if you don’t use them, you can’t cultivate any crop,” said Mane, who has been farming for three decades and now sprays chemicals on his cauliflower and cabbage weekly. He started out using dimethoate, then switched to another insecticide that only controlled the pests for about two years, he said. He has boosted the dosage, but heavier spraying has not solved the problem.
Pests and diseases reduce global crop yields by an estimated 20-40% every year, causing $220 billion in losses. Pesticide use in agriculture more than doubled worldwide between 1990 and 2024, reaching 3.92 million metric tons of active ingredients, according to the UN’s Food and Agriculture Organization.
Researchers have found that in some pest species, biological mechanisms that help them tolerate extreme heat can also help them withstand pesticides.
So as pests grow more resilient, experts say farmers also need to adapt. Many recommend integrated pest management, which includes monitoring fields and spraying only when it makes economic sense rather than on a calendar schedule. Farmers also should use natural predators to control pests. They need to adjust planting windows and, where available, choose crop varieties that better resist pests. Rotating chemical pesticides is recommended, as is taking care to make sure that pesticides do not kill off pollinators and other beneficial organisms.
But an integrated approach is difficult for smallholder farmers with limited access to training and resources.
“Poor farmers like me are left with no resort but to keep spraying,” Mane said.
Research from other countries points to similar concerns. A review study of African smallholder farming found that changing climatic conditions can increase pest problems and crop-loss risks in cotton, tomato, maize and cowpea.
Why some pests become harder to control
Warmer temperatures do not make every pest more resistant. In some cases, in fact, it’s the opposite. But in general, as temperatures rise, pests are expanding into new areas, appearing earlier in the season, or producing more generations in a year. Warmer conditions can cause some insects to develop faster.
When insects mature faster and produce the next generation more quickly, pesticide resistance can evolve more rapidly because resistant individuals have more opportunities to survive pesticide exposure and pass resistance traits to their offspring.
“In regions experiencing frequent heat waves, we could certainly see a decline in insecticide efficacy over time,” said Aline Guidolin, an entomologist and professor at the University of São Paulo’s Luiz de Queiroz College of Agriculture.
Global warming will not help all pests. In places where pests are already close to the highest temperatures they can tolerate, extreme heat can make some pests less successful, said Sanford Eigenbrode, an entomologist and professor emeritus at the University of Idaho. However, he added, “In temperate latitudes, warming is more likely to increase pest developmental rates, making them more difficult to control.”
One species that has developed resistance is the diamondback moth, a major pest of cabbage, cauliflower and other related crops. The past 50 years of global warming have expanded the area where it could survive winter by about 2.4 million square kilometers. Researchers have found that, on average, pesticide resistance levels were 158 times higher in areas where the moth could survive winter than in areas where it occurred only seasonally.
How warming can reshape pesticide resistance
Pesticide resistance depends on several factors, Eigenbrode said, including frequency of exposure, pre-existing resistance traits in a population, breeding and development characteristics, and the level of annual exposure.
“Warming climates can alter these factors,” he said.
Rising temperatures or other environmental factors can change which versions of certain genes become more common in a pest population. Evolutionary biologist Henry Chung, an associate professor at Michigan State University, said certain genes may be involved in both heat tolerance and insecticide resistance. Changing environmental conditions can make these gene versions more or less common over generations. This could make a population more or less resistant to insecticides.
“Environmental change can cause populations to be more resistant to an insecticide, or it can also cause populations to be more susceptible,” Chung said.
A pest could even become more resistant to one insecticide while becoming more susceptible to another.
Heat makes resistant pests harder to kill
In Brazil, researchers tested fall armyworms, a major maize pest, between 18°C and 32°C, comparing insects resistant to two insecticides with those that were not. At 28°C, they needed a concentration 340 times higher of spinetoram insecticide to kill resistant armyworms than they did to produce the same mortality level in susceptible insects.
At 32°C, the difference grew to nearly 590 times.
Guidolin, who co-authored the study, said that at higher temperatures, the armyworms’ metabolism speeds up, allowing them to break down and detoxify insecticides faster. Higher temperatures enhance this defense mechanism, she said, making insecticides like chlorantraniliprole and spinetoram less effective.
To manage the growing challenge of pesticide resistance, Guidolin said farmers should follow insecticide-resistance management practices, including applying insecticides only at manufacturer-recommended rates, avoiding under-dosing and over-dosing. Farmers should also rotate between pesticides that work in different ways.
Still, “As temperatures rise, chemical rotation alone won’t be enough,” she warned.
Sanford recommends switching between pesticides that target pests in different ways, while protecting beneficial organisms, including pollinators.
Researchers try switching off genes that build resilience
Researchers in China studied Tetranychus truncatus, a spider mite that attacks more than 100 crops, including maize, cotton and soybean. They identified five genes involved in producing heat-shock proteins, which protect cells from stresses such as extreme heat and pesticides. Three of the genes became much more active at 38°C to 42°C. Two also became more active after exposure to sublethal doses of three acaricides.
When the team switched off these two genes, the mites became more vulnerable to both heat and acaricides. Mortality increased by up to 35% under heat, and by up to 38.8% after pesticide exposure, showing that the same biological defenses that help the mites cope with heat can also help them withstand pesticides.
Farmers facing increasingly difficult pest-control challenges need solutions that protect their crops while slowing the development of pesticide resistance.
Raosaheb Yadav, 65, has cultivated cabbage since 1978. He grows three cabbage crops a year and said global warming has made each cycle harder. Pest numbers have increased, and so have the varieties of pests, forcing him to rely on more chemicals. He used to spray every 10 days; now he sprays more than once a week, he said.
He said farmers can no longer wait to spray until they see pests in their fields: “You miss one window, and the next day you will see several pests.”
To make matters worse, some of the insecticides he once relied on have also stopped working effectively, forcing him to use higher concentrations and add a sticker, an additive that helps the pesticide adhere to the plant surface and reduces the amount washed away by rain or irrigation.
The integrated practices recommended by experts could reduce unnecessary pesticide use and slow the development of resistance, but Yadav said he feels unable to weather any short-term losses that could come with switching tactics.
“A farmer can’t afford any losses here because the cost of production is already so high,” he said. If the pests do not die, farmers have little choice but to find another pesticide. “I never imagined pest control would become this difficult.”
Source - https://yaleclimateconnections.org
