The Value of Bats to Crop Production and Revenue

Let's take a moment to consider iconic animals that can be common in Pennsylvania: bats. Bats are often feared or misunderstood because they are nocturnal and associated with various myths, but if you learn about them, you will quickly see that bats should be respected and valued in part because of the positive influence they have on agriculture.

Because bats eat insects, they are extremely important for pest control. Specifically, bats prefer to eat moths, whose offspring are often crop-eating caterpillars, like corn earworm, black cutworms, and armyworms, among many others. A decade ago, researchers in Illinois conducted a two-year experiment in corn fields that revealed that bats save about $1 billion in crop damage per year. During this experiment, researchers used large field cages to exclude bats at night from the airspace above research plots while allowing them access to others. These cages were in place for about three months during each of the two field seasons. When bats did not have access to the airspace above corn fields, corn earworm populations were about 60% higher, and earworms damaged about 50% more kernels than plots that bats could not access. Further, due to corn earworm feeding, fungal infestations of corn ears were much higher where bats were excluded, so an absence of bats can indirectly exacerbate fungal infestations! This research clearly indicates that having bats around benefits crop production. Thus, we should want Pennsylvania to have healthy bat populations that can limit how many caterpillars infest crop fields.

Unfortunately, several species of bats in Pennsylvania and the U.S., more generally, are suffering from a fungal disease called white nose syndrome that is decreasing their populations. In some places, 90 to 100% of bats have died from the disease. This outcome is, of course, terrible for bats as key members of natural ecosystems, but it is also bad for agriculture. In fact, lower bat populations because of the spread of white nose syndrome have allowed researchers to further explore the value of bats for agriculture. This research compared insecticide use from years when bat populations were healthy to recent years when populations were much lower. Surprisingly, the research found that with fewer bats, insecticide use by farmers increased by 31% because more caterpillars and other insects are infesting fields. Unexpectedly, this increase in insecticide use was accompanied by an 8% increase in human infant mortality rates in those areas that received more insecticides, indicating that those areas experienced more environmental pollution and associated health challenges. If that is not bad enough, the researchers were able to detect about a 30% decline in crop revenues in areas with fewer bats, in part because of lower yield due to pests and the higher insecticide costs.

This information is sobering but emphasizes that unexpected forces can influence crop management practices and farm success. Farmer profitability and human health are suffering the consequences of a fungal disease decimating bat populations—an issue that is well beyond the control of farmers. The lesson here is that everything is connected, and healthy ecosystems benefit agriculture, but it is also true that conservation-based farming can minimize the impact of farming on the habitats and communities near farms.

So, what can farmers do? They can minimize insecticide use as much as possible to decrease risks to environmental and human health around their properties—adopting integrated pest management and using insecticides only when necessary would be a key step in the right direction. Other steps could include protecting natural areas on farms, including maintaining hedgerows, woodlots, and other non-crop areas where bats and other wildlife might spend some time. Farmers could also consider increasing diversity on their farms. Research has demonstrated that cropping areas with higher levels of plant species diversity and more complex crop rotations, including no-till and cover crops, tend to have fewer insect pest problems. Finally, it is crucial to respect the bats that we have left and hope that ongoing efforts to help bat populations are successful so that in the coming years, bats return to help control agricultural pests.