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With the emerging role of systems biology in understanding complex diseases affecting the brain, the heart and the body, the study of ecosystems in nature and in our gut – and the implication of alterations in these ecosystems – has become a major focus of medical research (see MGC podcast episode with Nathan Price).

An ecosystem is a community of living organisms including plants, animals and microbes interacting with their environment. These organisms are linked together through nutrient cycles and energy flows, forming a complex system where all living things in a particular region depend on each other and their surroundings to survive.

An article by Eyal Frank, from the Harris School of Public Policy, University of Chicago, Chicago, IL, USA, the Center for Economic Policy Research, Paris, France and the National Bureau of Economic Research, Cambridge, MA, USA was recently published in the prestigious journal SCIENCE, titled “The Economic Impacts of Ecosystem Disruptions: Costs from Substituting Biological Pest Control”.

This article highlights the significant role that biodiversity and natural ecosystems play in human health and in agriculture. It focuses on the impact that declining bat populations have on farmers and human health due to the emergence of a disease called White-Nose Syndrome (WNS), which affects insect-eating bats.

“Natural ecosystems provide numerous services that benefit human society…”

Natural ecosystems provide numerous services that benefit human society, one of which is biological pest control. Insect-eating bats play a crucial role in this process by controlling insect populations that could otherwise damage crops. However, over the past few decades, biodiversity has been rapidly declining, and ecologists have theorized that disruptions in ecosystem functioning could have severe consequences for agriculture and human health.

“Chemical fertilizers used extensively in agriculture suppress nature’s factory of disease fighting molecules…”

As discussed extensively in my book, The Mind Gut Immune Connection, another important area where this theory applies is the ecosystem made up of plants, soil microbes and pests.

Soil microbes interact with the root system of plants, stimulating the plants to produce insect- and disease-fighting polyphenols. Chemical fertilizers used extensively in agriculture suppress nature’s factory of disease-fighting molecules, making these plants more vulnerable to diseases and infections, and resulting in the need for more and more chemical pesticides to keep the plants healthy.

The study by Frank and colleagues takes advantage of a natural experiment resulting from the outbreak of WNS, a disease caused by an invasive fungus that has devastated bat populations in the United States. The disease began spreading in 2006 and has since affected 12 of the approximately 50 insectivorous bat species in the U.S., leading to drastic declines in bat numbers. As bat populations dwindle, farmers have had to turn to synthetic insecticides to control pest populations. The use of these chemicals, however, comes with its own set of health risks.

The research aims to quantify the economic and health impacts of declining bat populations by focusing on three primary outcomes:

1. The increase in insecticide use by farmers.
2. The subsequent rise in infant mortality rates due to higher insecticide exposure.
3. The broader economic costs to agricultural operations, including changes in farm revenues and chemical expenditures.

The study leverages county-level data from areas affected by the bat disease to compare changes in agricultural practices and human health outcomes before and after bat populations were impacted by the disease. Below are the major findings of the study:

“In counties where bats have been decimated by WNS, farmers increased their use of insecticides by approximately 31% on average.”

In counties where bats have been decimated by WNS, farmers increased their use of insecticides by approximately 31% on average. Even though the findings don’t prove causation, they support the idea that bats provide an essential service in controlling pest populations, and when they are no longer available, farmers must compensate by using more chemicals to protect their crops.

The rise in insecticide use was associated with a 7.9% increase in infant mortality rates in affected counties. This increase in infant deaths is primarily attributed to the toxic effects of insecticides, which can pollute water and soil and become airborne, posing a risk to human health even when used according to regulatory guidelines. Infants, with their evolving brain gut microbiome system are particularly vulnerable to the adverse short and long-term effects of pesticide exposure.

“When combined with the estimated costs of increased infant mortality, the total economic damage rises to $39.4 billion from 2006 to 2017.”

Beyond the human health impacts, the loss of bats has significant economic repercussions. The decline in biological pest control forces farmers to spend more on insecticides, while simultaneously experiencing a drop in crop quality and farm revenues. The study estimates that the total agricultural losses due to WNS in affected counties amount to $26.9 billion (in 2017 dollars). When combined with the estimated costs of increased infant mortality, the total economic damage rises to $39.4 billion from 2006 to 2017.

The findings of this study validate previous ecological and economic theories that biodiversity loss can impose substantial costs on human health and well-being. In the case of bats, their role in controlling insect populations is not easily or safely replaced by synthetic insecticides, which, while effective at reducing pest damage, come with significant health risks and economic costs.

The same argument holds for the increasing use of chemical insecticides used to fight pests in plants devoid of their own disease fighting mechanisms as a consequence of increasing use of chemical fertilizers.

“The study highlights the importance of maintaining healthy ecosystems both in our environment and within our bodies.”

The findings suggest that current regulations on pesticide use may not be sufficient to protect human health, particularly in areas where nature’s own pest control services are in decline.

The article underscores the interconnectedness of natural ecosystems, agriculture, and human health, and stresses the urgent need for policies that take into account the full range of ecosystem services provided by biodiversity.