A fungal disease killing millions of bats across North America has been connected to higher infant mortality rates in affected areas, according to new research published in the journal Science.
Bats eat insects, thus providing free pest control services to many farms. The study found that when bat populations crashed due to the white-nose syndrome fungal disease, farmers compensated by increasing insecticide use by 31%. This change corresponded with a nearly 8% rise in infant mortality rates in affected U.S. counties.
“[The author] uses simple statistical methods to the most cutting edge techniques, and the takeaway is the same,” Eli Fenichel, an environmental economist from Yale who was not involved in the study, said in an interview with The New York Times. “Fungal disease killed bats, bats stopped eating enough insects, farmers applied more pesticide to maximize profit and keep food plentiful and cheap, the extra pesticide use led to more babies dying. It is a sobering result.”
Eyal Frank, the author of the study from the University of Chicago, told Mongabay that the gradual expansion of white-nose syndrome across the U.S. serves as a natural experiment to study how the loss of bats’ pest control affected agricultural practices and public health.
The infant mortality rate, or the number of infant deaths before their first birthday, is often used as an indicator of a society’s overall health. The research found that for every 1% increase in insecticide use, infant mortality increased by 0.25%. This equates to 2.5 infant deaths per 1,000 live births.
In the 245 counties affected by white-nose syndrome between 2006 to 2017, Frank estimated the number of infant deaths to be 1,334.
Frank looked into alternative explanations that might explain this, including weather variation, changes in crop composition and unemployment conditions. He also excluded accidents and homicides and examined whether other causes of death, such as those linked to the opioid epidemic, changed systematically in counties affected by white-nose syndrome. None of these factors explained the observed increases in infant mortality.
He was not surprised, he said. “These findings agree with previous estimates on environmental pollution and infant health.”
Several studies have found connections between pesticides and infant health. A 2023 systematic review reported pesticides found in maternal serum, placenta and umbilical cord.
Frank’s study is particularly significant because it shows health impacts occurring at a population level, even when farmers followed the rules about how much pesticide they could legally use. This suggests “the difficulties of assessing the public health impacts of pesticides when regulating them individually,” Frank said. While each pesticide might be considered safe on its own, the combined effect of using multiple pesticides or using them more frequently could still pose health risks.
The study estimates total damages, including agricultural losses and health impacts, at $39.4 billion across affected counties from 2006 to 2017. This figure combines $12.4 billion in health-related damages plus $26.9 billion in agricultural losses due to decreased crop revenue and increased chemical costs. (After white-nose syndrome appeared, insecticide use increased by about 1 kilogram [2.2 pounds] per square kilometer [0.4 square miles] compared with unaffected counties, growing to more than 2 kg [4.4 lbs] per km2 after five years.)
And the issue could be getting worse. A new report from the North American Bat Conservation Alliance found that 52% of bat species in North America are at risk of extinction within the next 15 years.
White-nose syndrome, first detected in the northeastern United States in the mid-2000s, has devastated North American bat populations. The disease is caused by an invasive fungus that scientists believe hitched a ride from Europe on gear, clothing or shoes. The fungus, which appears as a white fuzzy growth on bats’ noses, ears and wings, is particularly deadly during hibernation.
“The fungus disrupts their ability to hibernate and go into those long bouts of torpor where they’re conserving their energy,” Winifred Frick, chief scientist at Bat Conservation International, who was not involved in the study, told Mongabay. “It often leads to real physiological costs that result in starvation.”
The disease has now spread to 40 U.S. states and nine Canadian provinces.