Agricultural insect pests cost the U.S. agricultural industry $33 billion per year in crop losses, and destroy approximately 25–50% of crops worldwide. This trend continues despite an increased use of pesticides in recent decades on farms throughout the world. Broad-spectrum pesticides are dangerous to human health, degrade ecosystem function, upset carefully optimized integrated pest management (IPM) programs, and devastate natural insect predators and parasitoids. In addition, the World Resources Institute estimates that up to 400 agricultural pest species may have evolved some degree of pesticide resistance.

One effort to limit pesticide includes the use of biological control agents, which are living organisms that prey upon pest species. While proven effective in some cases, biological control comes with significant economic costs and typically offers only partial control. Biological control agents are typically non-native species and may have long-lasting negative effects on native biodiversity.

Native generalist predators can effectively serve as agents of biological control. Temperate insectivorous bats are highly effective generalist predators, and studies have documented the presence of many agricultural pest species in their diet. Especially during the summer months, when bats are raising young, female bats consume a significant proportion of their body weight in insects per day. Because they feed within a few kilometers of their roost site and return to the same roost every day, bats may play an important role in local suppression of agricultural insect pests.

What Do Bats Eat?

Identifying the insect prey of bats is challenging. Historically, biologists analyzed bat fecal and stomach contents, which involved visually identifying undigested insect fragments. Recently, molecular techniques have allowed identification of insect DNA from bat feces (guano), providing much better information about what a bat eats.

We now know that the majority of a bat's diet consists of moths (lepidopterans), beetles (coleopterans), flies (dipterans), cicadas and leaf hoppers, and true bugs (hemipterans). These orders of arthropods include many important agricultural insect pest species. Some prominent examples include corn earworm moth (Helicoverpa zea), cotton bollworm (Helicoverpa zea), spotted cucumber beetle (Diabrotica undecimpunctata), western corn rootworm (Diabrotica virgifera), and three stinkbug species: green stinkbug (Acrosternum hilare), brown stink bug (Euschistus servus), and brown-marmorated stinkbug (Halyomorpha halys). A detailed list of insect pests in New Jersey known to be consumed by bats is included in Table 1.

Economic Importance of Bats

Bats provide an important ecosystem service through pest consumption, which is valued at $22.9 billion annually in the United States. The economic benefits of bats are usually estimated by examining the reduction of pesticide use and avoided costs of crop damage. For example, bats in south-central Texas eliminate the need for at least one application of insecticides on cotton fields, and reduce larval damage to crops, resulting in a net benefit of $741,000 per year. However, bats also contribute more subtle indirect benefits. For instance, bats reduce fungal infections of corn, which in turn, reduces negative impacts on the livestock that consumes it. Pesticide reduction also limits environmental damage and human health risk.

Bat-friendly Agricultural Practices

Modifying habitats to support natural insect predators like bats, termed "conservation biological control," has become a valuable component of integrated pest management (IPM) programs. Big brown bats (Eptesicus fuscus) and little brown bats (Myotis lucifugus) are the two species of bat most commonly found roosting in bat houses and man-made structures in New Jersey. Installing bat houses throughout a farm provides quality bat habitat for these species and can attract large maternity colonies if installed correctly.

Another bat-friendly agricultural practice is to support non-crop habitat such as woodlands, ponds, and meadows on the farm. While big brown and little brown bats do well in man-made structures, other species rely heavily on forested habitat. Maintaining tree lines and forest patches with a diversity of vegetation can help provide habitat for forest-dwelling species. Each bat species consumes a slightly different group of insects; therefore, supporting a diversity of bat species will help increase pest control benefits. In addition, avoiding deconstruction of old structures (i.e., barns) in which bats might be roosting, and keeping standing dead trees in place, can help maintain habitat availability for bats.

Conclusion

Researchers continue to use innovative methods to explore the role of bats as biological control agents. Increasing bat habitat on agricultural lands and in residential areas could promote insect suppression, as well as help to conserve these beneficial animals. For further information, please visit our website at wildlife.rutgers.edu or email us at wildlife@njaes.rutgers.edu.

References

• Boyles, J.G., P.M. Cryan, G.F. McCracken, and T.H. Kunz. 2011. Economic importance of bats in agriculture. Science 332: 41-42.
• Clare, E.L., E.E. Fraser, H.E. Braid, B. Fenton, and P.D.N. Hebert. 2009. Species on the menu of a generalist predator, the eastern red bat (Lasiurus borealis): using a molecular approach to detect arthropod prey. Molecular Ecology 18: 2532-2542.
• Cleveland, C.J., M. Betke, P. Federico, J.D. Frank, T.G. Hallam, J. Horn, J.D. Lopez Jr, G.F. McCracken, R.A. Medellin, A. Moreno-Valdez, C.G. Sansone, J.K. Westbrook, and T.H. Kunz. Economic value of the pest control service provided by Brazilian free-tailed bats in southcentral Texas. Frontiers in Ecology and the Environment 2006 4(5): 238-243.
• Dodd, L.E., E.G. Chapman, J.D. Harwood, M.J. Lacki, and L.K. Rieske. 2012 Identification of prey of Myotis septentrionalis using DNA-based techniques. Journal of Mammalogy 93(4):1119-1128.
• Kunz, T.H., E.B. De Torrez, D. Bauer, T. Lobova, and T.H. Fleming. 2011. Ecosystem services provided by bats. Annals of the New York Academy of Sciences 1223:1-38.
• Maine, J.J., and J.G. Boyles. 2015. Bats initiate vital agroecological interactions in corn. PNAS 112 (40):12438-12443.

December 2020