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The loss of biodiversity and ongoing damage to ecosystems impacts human well-being, an environmental economist has underlined. A new study has looked at the outbreak of a highly contagious disease that devastated bat populations across the United States from 2006-2017 and found that it led to a rise in deaths of human infants following increased pesticide use by farmers.
The study, published in the journal Science, found that the widespread decline of insectivorous bats has led to a sharp rise in pesticide use by farmers. The knock-on effect of this increased pesticide use has been a surge in infant mortality — about 1,334 deaths in affected counties, the study suggested.
The links were established by Eyal Frank, an assistant professor at the Harris School of Public Policy at the University of Chicago. His research quantified the benefits of insectivorous bats and assessed the impact of their decline on human well-being and the economic costs of farming.
The decline in bat populations also caused agricultural losses, reduced crop revenue and increased chemical costs totalling $26.9 billion for counties affected by WNS between 2006 and 2017, the study found.
Insectivorous bats provide vital ecosystem services by controlling pests biologically. However, a disease known as white-nose syndrome (WNS), caused by the fungus Pseudogymnoascus destructans, led to a major decline in bat populations in the study period.
The decline set off a chain reaction of environmental and human health impacts. The loss of this natural pest control service led to a 31 per cent rise in pesticide use, which in turn has been linked to a nearly 8 per cent increase in infant mortality in affected regions, the research found.
WNS, a cold-loving disease, forms clusters of white flakes around the bats’ noses, causing them to wake prematurely from hibernation. With limited food sources and increased calorie demands due to low temperatures, many infected bats fail to survive the winter, with mortality rates ranging from 33 per cent to 99 per cent. The disease has the potential to cause local extinctions within six years.
WNS has an average mortality rate exceeding 70 per cent and was first reported in the US in 2006. Since then, it has spread geographically among bat populations, affecting 12 of the 50 bat species found in the country. The fungus is believed to have originated in Europe and was likely introduced to the US through international trade and travel.
The gradual expansion of the disease provides a setting that approximates random manipulation of bat population levels, which allowed me to estimate how farm operations and human health change differentially before and after a location experiences a negative shock to biological pest control
Eyal Frank, author of the study
Previous research has demonstrated the role of bats as biological pest control, given their large populations and high predation rates on a wide range of insects, many of which are agricultural pests, Frank noted. “Insectivorous bats consume 40 per cent and above of their body weight in insects each night,” he observed.
The researcher used annual county-level data to record insecticide usage and found that, following the decline in bat populations, farmers significantly increased their use of insecticides. “This highlighted the substitution of a declining natural resource with a man-made input, providing the first empirical validation of a fundamental theoretical prediction in environmental economics,” the study said.
The study examined county-level data on annual infant mortality, a widely accepted indicator of negative health impacts caused by environmental pollution, to assess the potential health consequences of increased insecticide use. Further, the researcher focused specifically on deaths from internal causes, rather than accidents or homicides.
Frank concluded that, even when used within regulatory limits, real-world levels of insecticide use can have harmful effects on human health. His findings underscored the difficulty of assessing the public health impacts of pesticides when they are regulated individually.
In June of this year, Frank and researcher Anant Sudarshan also highlighted the impact of declining vulture populations in India, which they estimate led to the deaths of 500,000 people. Their study revealed that the collapse of wild bird populations, which previously scavenged on rotting meat, contributed to the spread of infectious diseases, including rabies.