The Economic Impacts of Ecosystem Disruptions: Costs from Substituting Biological Pest Control

by Eyal Frank

Context

Biodiversity loss is accelerating, yet little is known about how these ecosystem disruptions impact human wellbeing. Bats, widely known to consume large numbers of insects, are one example of how wildlife and society interact. Farmers have come to rely on bats to provide a natural alternative to pesticides that protects their crops from insects that could harm them. In fact, previous research has suggested that bats provide farmers in the United States with billions of dollars annually from avoided crop losses because of their pest control.  Without bats, farmers might need to switch to a chemical pesticide, which have been linked to negative health impacts. Further, chemical pesticides might not fully substitute for the quality of pest control provided by bats, which could then impact the quality and value of crops and lead to lower crop revenue. This study provides empirical evidence on how disruptions to an ecosystem, such as the decline in bat populations, can have meaningful social and human health costs.

Research Design

Since 2006, White-Nose Syndrome—a disease fatal to bats caused by an invasive fungus found in the caves bats use during the day and throughout winter—has led to the collapse or near collapse of bat populations in counties in North America. The author uses the sudden emergence of White-Nose Syndrome, and subsequent bat die-offs, to conduct a natural experiment where counties experience “as good as random” sharp declines in their bat population levels. He compares the effect of bat die-offs on pesticide use in counties that experienced those bat population declines to counties that have likely not been affected by the wildlife disease, and tracks the change over time. He also tracks the impacts on infant mortality—commonly used to study negative health impacts of environmental pollution—to test for the potential health consequences of increased pesticide use. The author also estimates the amount of land used in agricultural production and crop sales before and after the bat die-offs.

Findings

When bat populations declined, farmers increased their use of pesticides by about 31 percent.

Farmers increased their use of chemical pesticides in the years following the detection of White-Nose Syndrome in their community, compared to counties where the disease was not detected. Over the span of one year since White-Nose Syndrome detection, farmers increased their pesticide use by 1 kilogram per squared kilometer; they increased it by 2 kilogram per squared kilometer five years after detection. On average, the author finds that farmers compensated for bat declines by increasing pesticide use by 31.1 percent.

When farmers increased their use of pesticides, the infant mortality rate rose by 7.9 percent.  

Because wind and water erosion can carry pesticides away from farmland and contaminate local waters, it has been linked to negative health impacts. In the years following the White-Nose Syndrome detection, the infant mortality rate increased by 7.9 percent in counties that experienced bat die-offs, or an additional 1,334 infant deaths. When aligning the data with the increase in pesticide use, the author found that when pesticide use increased by 1 percent, the infant mortality rate increased by 0.25 percent. The author used the mortality reduction value used by the US Environmental Protection Agency (also referred to as the value of statistical life) to estimate that between 2006 and 2017, the decline in bat populations resulted in USD 12.4 billion (2017 dollars) in total infant mortality damages.

The quality of the crops declined, and farmers saw their revenue cut by nearly 29 percent.

The study found that pesticides aren’t as good at preventing pests as bats. While the amount of land used to grow crops didn’t change after the emergence of White-Nose Syndrome, the quality of the crops likely did decline. As a result, crop revenue decreased by nearly 29 percent. The author estimated that, between 2006 and 2017, the decline in bat populations resulted in USD 26.9 billion (2017 dollars) in total agricultural, crop revenue, and chemical expenditure losses for communities that experienced the bat die-offs.

Closing Take-Away

Making informed decisions about conservation regulations, policies and funding requires rigorous evidence, including the need for increased monitoring and accessible data on chemical pollutants like pesticides and wildlife monitoring. This study underscores how species interactions can extend beyond an ecosystem, with outcomes affecting agriculture, human health, and the economy.