Bats are thought to provide valuable services to agriculture by suppressing crop pests, but their ecological role in agricultural systems remains unclear. We implemented a unique field experiment to assess the ecological and economic effect of bats in corn agriculture and found that bats initiated strong and surprising ecological interactions in corn fields. Bats not only suppressed crop pest numbers and crop damage but also indirectly suppressed the presence of pest-associated fungus and a toxic compound produced by the fungus. As nocturnal flying insectivores, bats occupy unique ecological roles and provide valuable services to society, and it is therefore essential that we conserve this often-maligned group.
Abstract
In agroecosystems worldwide, bats are voracious predators of crop pests and may provide services to farmers worth billions of U.S. dollars. However, such valuations make untested assumptions about the ecological effect of bats in agroecosystems. Specifically, estimates of the value of pest suppression services assume bats consume sufficient numbers of crop pests to affect impact pest reproduction and subsequent damage to crops. Corn is an essential crop for farmers, and is grown on more than 150 million hectares worldwide. Using large exclosures in corn fields, we show that bats exert sufficient pressure on crop pests to suppress larval densities and damage in this cosmopolitan crop. In addition, we show that bats suppress pest-associated fungal growth and mycotoxin in corn. We estimate the suppression of herbivory by insectivorous bats is worth more than 1 billion USD globally on this crop alone, and bats may further benefit farmers by indirectly suppressing pest-associated fungal growth and toxic compounds on corn. Bats face a variety of threats globally, but their relevance as predators of insects in ubiquitous corn-dominated landscapes underlines the economic and ecological importance of conserving biodiversity.
Published on September 14, 2015In agroecosystems worldwide, bats are voracious predators of crop pests and may provide services to farmers worth billions of U.S. dollars. However, such valuations make untested assumptions about the ecological effect of bats in agroecosystems. Specifically, estimates of the value of pest suppression services assume bats consume sufficient numbers of crop pests to affect impact pest reproduction and subsequent damage to crops. Corn is an essential crop for farmers, and is grown on more than 150 million hectares worldwide. Using large exclosures in corn fields, we show that bats exert sufficient pressure on crop pests to suppress larval densities and damage in this cosmopolitan crop. In addition, we show that bats suppress pest-associated fungal growth and mycotoxin in corn. We estimate the suppression of herbivory by insectivorous bats is worth more than 1 billion USD globally on this crop alone, and bats may further benefit farmers by indirectly suppressing pest-associated fungal growth and toxic compounds on corn. Bats face a variety of threats globally, but their relevance as predators of insects in ubiquitous corn-dominated landscapes underlines the economic and ecological importance of conserving biodiversity.
Research published in the Proceedings of the National Academy of Sciences today confirms that bats play a significant role in combating corn crop pests, saving more than $1 billion a year in crop damages around the world. Bat Conservation International funded the two-year experiment in cornfields near Horseshoe Lake in Southern Illinois, conducted by graduate student Josiah J. Maine and his adviser at Southern Illinois University Carbondale, Justin Boyles.
To investigate the value of bats as agricultural pest control, Maine used custom built “exclosures” – netted structures aimed at keeping bats outside of them and away from the corn.
“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 said. “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.”
Keeping the bats out meant pests, such as the corn earworm, were largely free to reign havoc on the corn crops. But bats are not the only predators of these agricultural pests. To ensure only bats were excluded by the exclosures Maine moved the structures twice daily so birds could forage normally.
After analyzing the results, Maine said he found nearly 60 percent more earworm larvae inside the exclosures – protected from the hungry bats – than in the unprotected control areas. He also found more than 50 percent more corn kernel damage per ear in the corn inside the exclosures.
“By consuming crop pests, bats have tremendous ecological impacts in crop fields. Based on the difference in crop damage I observed, I estimated that bats provide a service to corn farmers worth about $1 billion globally” Maine said.
In addition to controlling pest populations, bats were also found to suppress pest-associated fungal growth found in corn— a money-saving agricultural service not reflected in Maine’s suggested estimate.
“This was sort of a serendipitous discovery of this research,” Maine said. “I found that [bats] seemed to be suppressing the population of crop pests and thereby suppressing the abundance of the toxic fungus and also the toxins produced by that fungus.”
The implication of these findings serves as great news for agriculture and bat conservation alike said 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.”
Boyles also hailed the study and its implications. “[This research] highlights the importance of maintaining a healthy and high functioning ecosystem,” said Boyles. “Bats are much maligned, but deserve protection if for no other reason than the ecosystem services they provide to humans.”
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