By Ron Hammond and Andy Michel, Ohio State University Extension entomologists
Recently, white-nose fungus was detected among bat populations in Ohio. White-nose fungus is a new disease of bats that is expanding westward across the country. It is a very serious pathogen that tends to awake bats during hibernation. Infected bats are then unable to hibernate and cannot survive the winter, causing massive mortality in bat populations. It is feared that white nose fungus will lead to local extinctions. Losing native bat populations is serious in of itself, but many species provide a valuable service — devouring insects. Most of what these bats eat includes mosquitoes, flies, and even some agronomic crop pests such as European corn borer and various corn rootworm species. Bats are an important part of a group of general predators that include both insects and vertebrates. For example, birds have been known to remove corn ear worm or western bean cutworm from infected ears. While one species of predator may not economically control a pest by itself, the loss of many members of the group of crop pest predators is important and has the potential to decrease natural control.
A recent article appearing in Science, a well know scientific publication, and placed in numerous newspapers, suggests that the loss of bats due to this disease would cost crop growers billions of dollars across the United States, with the cost to Ohio growers $1.7 billion.
While this disease is a serious threat to Ohio’s bats, the impact on Ohio’s field crops is questionable. The amount of crop loss suggested was solely based on a single study on cotton in southwest Texas with one bat species, the Brazilian free-tailed bat, feeding on one pest species, the cotton bollworm, also known as the corn earworm. While the corn earworm does migrate from southern states and occurs in Ohio, it is mostly a concern on sweet corn and other vegetables. The Brazilian free-tailed bat is not found in Ohio. The potential cost to Ohio’s growers was extrapolated from this single study done in Texas. And upon reading this study from Texas, most of its conclusions were based on associations between the bat and this one pest, various assumptions, and numerous further extrapolations. Although the commonly found bats in Ohio are known to feed on crop pests during the summer, none are thought to play a significant role in keeping crop pest numbers down by themselves. At most, they probably just add to general pest predation from various insect predators including other vertebrates such as birds and various beneficial insects. Perhaps research in the future might alter our knowledge of this, but at this time, field crop growers should not be overly concerned. However, bats are an important component of the ecosystem, and white-nose fungus is a serious threat to their survival.