The Guardian reports on a study of knock-on effects. Bat populations have been decimated in the U.S. and beyond by the white-nose fungus. Because bats eat mosquitoes (which carry disease) and other insects (which destroy crops), the declining bat population has led to an increase in crop failures, sickness, and — most significantly — pesticide use… which in turn can be mapped onto an 8% increase in infant mortality in the worst-hit areas:
When Eyal Frank, an assistant professor at the University of Chicago, learned about the disease, called white-nose syndrome, he realised it provided a perfect natural experiment to demonstrate the value of a bat. Bats eat 40% or more of their bodyweight in insects every night, including many crop pests. What would their disappearance mean?
In infected areas, he found, farmers compensated for the loss of bats by significantly increasing their use of insecticides – by 31.1% on average.
Next, Frank looked at infant mortality – a metric commonly used to judge the impact of environmental toxins. Infected counties had an infant death rate 7.9% higher, on average, than counties with healthy bats, despite pesticide use being within regulatory limits. That equates to 1,334 extra infant deaths.
Frank tested other factors that might plausibly explain the rise in deaths: unemployment, the opioid epidemic, the weather, differences among mothers, or the introduction of genetically modified crops, but none explained the increase in pesticide use or the rise in infant deaths. He spent a year “kicking the tyres on the study”, and the results held. It provided “compelling evidence”, he said, “that farmers did respond to the decline in insect-eating bats, and that response had an adverse health impact on human infants”.
It is unusual for a study of this type to suggest causation, not just correlation, said [Harvard researcher Charles] Taylor [who was not part of this study].
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The findings on pesticide use also echo previous research, including a study of Taylor’s. In the US, cicadas emerge en masse at intervals of 13 to 17 years. Taylor found that pesticide use increased in cicada seasons, as did infant mortality. People born in cicada years had lower test scores and were more likely to drop out of school.
You can read Frank’s research here, in Science, and Taylor’s cicada research here.