Billion-dollar Bats

In the grassy cornfields of Southern Illinois, bats are on the hunt for insects, and according to new research, farmers have a billion reasons to be grateful for it.

BCI-funded research recently published in the Proceedings of the National Academy of Sciences confirms that bats play a significant role in combating corn crop pests, preventing more than $1 billion in crop damages around the world every year. This figure is based on a two-year experiment conducted in cornfields near Horseshoe Lake in Southern Illinois by graduate student Josiah J. Maine and his adviser at Southern Illinois University Carbondale, Justin Boyles.

Maine conducted the experiment over the 2013 and 2014 growing seasons to test how corn fared with and without bats picking off various pests. To do this, he built “exclosures”—netted structures aimed at keeping bats outside of them and away from the corn. The exclosures were large; each enclosed crops in an area greater than 4,200 square feet and 23 feet high.

Keeping the bats out meant pests, such as the corn earworm, were largely free to wreak havoc on the corn crops. But bats are not the only predators of these agricultural pests. So to factor in these other variables, Maine went to great lengths to ensure that only bats were excluded by the structures.

“The exclosures had to be removed daily so birds could forage normally,” Maine says. “I arranged the netting so it could be slid on the cables to one end like a shower curtain. This way I could open the exclosures each day and close them each night,” before the bats took to the air.

In all, Maine built six exclosures, each of which was paired with a control plot where bats could forage as they normally would. This arrangement allowed him to directly compare pest abundance and crop damage between the exclosure and control plots.

“The main pest in my system was the corn earworm, a moth whose larvae cause billions of dollars’ worth of damage to corn, cotton, tomatoes and many other crops,” Maine says. “The larvae feed on corn ears, causing direct damage to yield, but they also can introduce an avenue for infection of the corn ear by fungi, which produce compounds that are toxic to humans and livestock.”

While bats were known to feed on the adult moth of the corn earworm, this is the first study to directly document that they consume enough of the moths to suppress larval populations and damage to corn.

After analyzing the results, Maine notes that he found nearly 60 percent more earworm larvae inside the exclosures—where they were protected from the hungry bats—than in the unprotected control areas. He also found:

• 50 percent-plus more corn kernel damage per ear in the corn inside the exclosures;
• that the damaging fungal growth associated with pests was significantly higher on the corn inside the exclosures; and
• that the toxins produced by the fungus were much more concentrated in the corn inside the exclosures.

“By consuming crop pests,” Maine adds, “bats have tremendous ecological impacts in crop fields. Based on the difference in crop damage I observed, I estimated that bats annually provide a service to corn farmers worth about $1 billion globally. Bats likely provide additional value to agriculture by suppressing toxic fungi and reducing necessity for costly insecticides.”

The implication of these findings serves as great news for agriculture and bat conservation alike, stresses BCI Executive Director Andrew Walker: “Corn is an essential crop for farmers on over 150 million hectares globally. This research shows that by protecting bat species and their habitats we are not only furthering conservation, but also helping to secure a vital food source for communities worldwide.”

Already, the symbiotic relationship between farmers and bats seems to be taking shape.

“I’ve had some interaction with the local farmers in Southern Illinois, and from what I can tell, they are very interested in the impact of bats on their farms, because it directly impacts their bottom line and the value of their crops,” Maine says. “My study provides strong support for the idea that bats provide valuable services to society.”

A-MAIZE-ING BATS

To read an abstract or full-text version of the research, visit pnas.org and enter the author’s name into the search box.