The connections are commonsense but the conclusion is shocking.
Bats eat insects. When a fatal disease hit bats, farmers used more pesticides to protect crops. And that, according to a new study, led to an increase in infant mortality.
According to the research, published Thursday in the journal Science, farmers in affected U.S. counties increased their use of insecticides by 31 percent when bat populations declined. In those places, infant mortality rose by an estimated 8 percent.
“It’s a seminal piece,” said Carmen Messerlian, a reproductive epidemiologist at Harvard who was not involved with the research. “I actually think it’s groundbreaking.”
The new study tested various alternatives to see if something else could have driven the increase: Unemployment or drug overdoses, for example. Nothing else was found to cause it.
Dr. Messerlian, who studies how the environment affects fertility, pregnancy and child health, said a growing body of research is showing health effects from toxic chemicals in our environment, even if scientists can’t put their fingers on the causal links.
“If we were to reduce the population-level exposure today, we would save lives,” she said. “It’s as easy as that.”
The new study is the latest to find dire consequences for humans when ecosystems are thrown out of balance. Recent research by the same author, Eyal Frank, an environmental economist at the University of Chicago, found that a die-off of vultures in India had led to half a million excess human deaths as rotting livestock carcasses polluted water and spurred an increase in feral dogs, spreading waterborne diseases and rabies.
“We often pay a lot of attention to global extinctions, where species completely disappear,” Dr. Frank said. “But we start experiencing loss and damages well before that.”
To come up with his findings, Dr. Frank analyzed county-level data on the detection of white-nose syndrome in bats, pesticide use by farmers and a variety of health indicators, including infant mortality. Two environmental economists who were not involved with Dr. Frank’s study, Jason Shogren of the University of Wyoming and Eli Fenichel of Yale, praised the methodology and the efforts Dr. Frank made to seek a different explanation for the uptick in both insecticides and infant mortality.
“He uses simple statistical methods to the most cutting edge techniques, and the takeaway is the same,” Dr. Fenichel said. “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.”
Dr. Frank estimated the number of infant deaths at 1,334 throughout 245 counties affected by white-nose syndrome from 2006 to 2017.
Three species of bats in North America have been decimated by white-nose syndrome, a disease caused by a fungus that attacks the animals during hibernation. Researchers first discovered sick and dying bats with white fuzz on their noses, ears and wings in the Northeast in the mid-2000s. The fungus can live on clothes, shoes and gear, which is how scientists believe it arrived in North America, probably from Europe. Since then, bats with white-nose syndrome have been confirmed in 40 states and nine Canadian provinces. Researchers are working to find ways to help bats survive the disease.