Bat population collapse linked to increased pesticide use, deaths of more than 1,000 infants

Bats are considered a natural pesticide, widely used by farmers as an alternative to chemical pesticides to protect their crops from insects. But since 2006, bat populations have collapsed in counties across North America due to an invasive fungus found in the caves the bats use during the day and throughout the winter, which causes what is known as white-nose syndrome.

A study in Science The study uses their sudden collapse to determine whether farmers resorted to chemical pesticides and whether this had an impact on human health. It found that farmers did indeed increase their use of pesticides, leading to the deaths of more than 1,000 infants.

“Bats have gotten a bad rap, especially since reports emerged of a possible link to the origins of COVID-19,” said study author Eyal Frank, an assistant professor at the Harris School of Public Policy. “But bats add value to society in their role as natural pesticides, and this study shows that their decline may be bad for humans.”

Frank compared the effect of bat mortality on pesticide use in counties that experienced these bat population declines to counties that likely weren’t affected by wildlife disease.

He found that when bat populations declined, farmers increased their pesticide use by about 31 percent. Because pesticides are associated with negative health effects, Frank then tested whether increased pesticide use corresponded with increased infant mortality, a common marker for studying the health effects of environmental pollution.

In fact, when farmers increased their pesticide use, the infant mortality rate increased by nearly 8%, which corresponds to 1,334 additional infant deaths. In other words, for every 1% increase in pesticide use, the infant mortality rate increased by 0.25%.

The study also found that pesticides are not as effective at preventing pests as bats. Crop quality likely declined, as farmers’ income from crop sales decreased by nearly 29 percent. When this income loss is combined with the cost of pesticides, farmers in communities that experienced bat extinctions lost $26.9 billion between 2006 and 2017. Adding to these losses the $12.4 billion in damages caused by infant mortality, the total societal cost of bat extinctions in these communities is $39.6 billion.

“When bats are no longer there to do their job of controlling insects, the costs to society are very high, but the cost of maintaining bat populations is probably lower,” Frank says.

“More broadly, this study shows that wildlife adds value to society, and we need to better understand this value in order to inform policies to protect them.”