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<\/div>A little brown bat (Myotis lucifugus<\/i>) with white-nose syndrome, which has ravaged bat populations across the US<\/p>\n
piemags\/FWL \/ Alamy Stock Photo<\/p>\n<\/div>\n<\/figcaption><\/figure>\n<\/p>\n
The decline of bats in the US due to the spread of a fungal disease reduced farmers\u2019 earnings and led to an additional 1300 deaths in children under 1 year old, a study has reported.<\/p>\n
In counties where the bat disease is present, farmers increased their use of insecticides by 31 per cent to make up for the reduction in insect predation by bats,\u00a0Eyal Frank<\/a> at the University of Chicago in Illinois found. Between 2006 and 2017, farmers in affected counties lost $27 billion as a result of lower crop sales and higher insecticide costs, he calculates.<\/p>\n What\u2019s more, in the affected counties, there was also an 8 per rise in the number of children dying before 1 year of age, which Frank attributes to the increase in insecticide use<\/a>.<\/p>\n \u201cInsecticides are toxic by design,\u201d he says. \u201cEven when they are used at regulatory levels, there seems to be a health cost.\u201d<\/p>\n In 2006, hibernating bats with a white fungus on their muzzles<\/a> were seen in a cave in New York state, with many dying. White-nose syndrome, as it is known, has been spreading across North America ever since, killing millions of bats<\/a>.<\/p>\n <\/p>\n When Frank read about white-nose syndrome, he realised it provided a way to directly assess the benefits that bats provide to farmers. \u201cThis is a very good approximation for an ideal experiment where one would go out and randomly manipulate populations,\u201d he says.<\/p>\n He has used data from agricultural censuses to compare counties where white-nose syndrome has been detected with those where it wasn\u2019t yet present up to 2017 \u2013 stopping that year because the census data is only released every few years.<\/p>\n In affected counties, insecticide use rose higher every year after the detection of the disease, but it remained broadly constant in other areas.<\/p>\n White-nose syndrome affects only 11 of the around 50 bat species in the US and has killed around 70 per cent of those species, on average, in affected areas, so the total value of bats to farmers in the US is far greater than the numbers Frank has calculated.<\/p>\n He then looked at data on infant mortality<\/a>, excluding deaths due to accidents and murders. The 8 per rise in affected counties would have resulted in an extra 1300 infant deaths by 2017, he calculates.<\/p>\n Frank thinks his findings go beyond correlation to show that the die-off of bats is the cause of both higher insecticide use and higher infant mortality. He says the compelling thing is that the trajectory of counties changed in the same way once the disease reached them, whatever the year the disease arrived.<\/p>\n However, exactly how higher insecticide use<\/a> led to higher infant mortality isn\u2019t clear. \u201cI can\u2019t say anything about the direct exposure mechanism, only that my results are not consistent with the idea of exposure through food,\u201d says Frank.<\/p>\n That leaves breathing in insecticides or contaminated water supplies as the most likely routes.<\/p>\n \u201cFrank convincingly demonstrates that in counties affected by white-nose syndrome, insecticide use increases compared to counties that are not affected,\u201d says Roel Vermeulen<\/a> at Utrecht University in the Netherlands.<\/p>\n However, Vermeulen says that the loss of income would lead to more stress in farming communities, and that this could also contribute to higher infant mortality. \u201cTherefore, it is questionable whether the observed effects on infant mortality can be solely attributed to increased insecticide use,\u201d he says.<\/p>\n \u201cThis study shows that bats can save human lives just by doing what they do best \u2013 eating insects,\u201d says Jennifer Raynor<\/a> at the University of Wisconsin-Madison.<\/p>\n \u201cMany wild animals are important for human health and well-being, and we are now beginning to understand that technology cannot always replace these benefits when they are lost,\u201d she says.<\/p>\n Vermeulen thinks the study also shows that we need to broaden the way we think about human health. \u201cIt emphasises the need to move from a human-centric health impact analysis, which only considers the direct effects of pollution on human health, to a planetary health impact assessment,\u201d he says.<\/p>\n Topics:<\/p>\n<\/section><\/div>\n