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Bats for Natural Pest Control

Bats have a bad reputation. In reality, bats can be a farmer’s best friend by providing free and effective pest control services over farm fields and orchards.

A Mexican free-tailed bat (Tadarida rasiliensis) eating a moth. Courtesy Merlin D. Tuttle, Bat
Conservation International, www.batcon.org.

Most bat species in the United States are generalist insect predators, which means they will consume most medium-sized flying insects. Determining exactly what insects bats eat is often difficult, since bats feed in the sky at night. Until recently, scientists studied the diet of bats by dissecting fecal pellets under a microscope and identifying insect fragments, such as pieces of exoskeletons or legs, that survived the digestive tract of the bat.

With the exception of hard-shelled insects, including some stinkbugs and beetles, this rarely allowed for identification of insects to species level. Scientists could confirm that bats ate moths but could not confirm that bats were consuming specific pests of economic interest.

Modern techniques in the field of genetics now allow scientists to recover DNA from fecal samples and identify the insect remains found in bat feces by sequencing the insects’ DNA. Using these modern techniques, bat researchers across the country have identified to species level almost 200 insects that are consumed by bats, and many of these insects cause substantial economic loss.

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Most of the insects consumed in the United States are beetles and moths. While it is generally the larval form of moths that damage crops, bats are benefiting the crops by consuming the adult flying forms, therefore preventing the insects from further reproducing.

Several of the most damaging agricultural pests consumed by bats include spotted cucumber beetles (also known as southern corn rootworms; (Diabrotica undecimpunctata), brown stinkbugs (Euschistus servus), beet armyworm (Spodoptera exigua), fall armyworm (Spodoptera frugiperda) and large yellow underwings (a cutworm species; Noctua pronuba). All of these pests are known to damage a variety of crops across the nation, including alfalfa, corn, cotton, rice, soybean, tobacco and many other fruits, vegetables and grasses, costing farmers and growers large sums of money in lost crops and pesticides. In addition to crop pests, bats also consume many insect pests responsible for destroying millions of trees nationwide, including Asiatic oak weevils (Cyrtepistomus castaneus), emerald ash borers (Agrilus planipennis), and gypsy moths (Lymantria dispar).

Research done at the University of Tennessee focuses on bat consumption of corn earworms (also known as cotton bollworms; Helicoverpa zea) in the corn and cotton fields of the Winter Gardens region of Texas. Corn earworm larvae are very destructive insects, damaging corn, cotton, tomatoes, tobacco, sunflowers, wheat, rice, and many other crops. In the Winter Gardens area, Mexican free free-tailed bats (Tadarida brasiliensis) live in summer colonies of hundreds of thousands of bats roosting in caves and under bridges. The research showed that bats save farmers $741,000 annually in just this one area by reducing the number of pesticide applications required, as well as reducing crop damage. Farmers in this region are benefiting greatly from the large colonies of bats that live naturally in the area and provide free pest-control services.

Housing for Bats

One way to encourage bat activity is by installing bat houses, similar to birdhouses, which will provide an artificial roost for native bat species. A few pecan growers in Georgia and Texas now have completely organic orchards where they do not need to spray expensive chemical insecticides because they installed bat houses in their orchards. Both orchards’ bat houses are now home to thousands of bats, mostly Mexican free-tailed bats, which protect the orchards from insect pests. Researchers at the University of Tennessee and Boston University showed that bats living on these orchards are consuming several crop pest species, including pecan nut casebearers (Acrobasis nuxvorella), hickory shuckworms (Cydia caryana), southern green stink bugs (Nezara viridula), and green stink bugs (Acrosternum hilare).

Pecan nut casebearers are only known to damage pecans and hickory shuckworms damage both pecans and hickory trees, so the pecan orchards are seeing direct benefits from the bats’ presence.

These two stink bug species attack many important food crops, so the presence of the large colonies of bats is benefiting the farm fields surrounding the pecan orchards as well.

This large bat condo can hold over 1,000 bats.

Some insects can hear the ultrasound calls of the bats and may avoid areas of intense bat activity. Bats are nature’s own pesticide and simply increasing the number of bats on an orchard or farm may deter activity of some insects. Bat houses provide one of the best ways to encourage the presence of these native, generalist predators. In addition to providing protection from insect damage, sizeable colonies of bats living in bat houses will produce large amounts of guano, which can be collected and used as fertilizer with naturally high levels of phosphorus and nitrogen.

Many farmers and growers have had great success in decreasing the damage of insects to their crops by installing bat houses. Bat houses come in a variety of styles and it is important to know what type of house is the most likely to attract bats in your area.

Many people are skeptical of encouraging large numbers of bats near their homes. Like all mammals, bats are capable of carrying rabies and other wildlife diseases, but as long as people do not handle bats, there is no reason to fear them. Contrary to the movies that portray bats as attacking people, bats generally avoid humans, preferring instead to search the night skies for insects to consume.

Funding for this project was provided by Bat Conservation International (BCI) through a NRCS Conservation Innovation Grant from the USDA. BCI is a nonprofit organization located in Austin, Texas whose mission is conserving the world’s bats and their ecosystems in order to ensure a healthy planet. Visit Bat Conservation International’s website for more information on bat houses and tips on how to install a successful bat house.

Veronica brown received her master’s degree in ecology from the University of Tennessee, where she currently works as a research coordinator. She is working with bat Conservation International to make scientific research on bat diets more accessible to farmers and growers.

By Veronica Brown. This article was originally published in the November 2011 issue of Acres U.S.A.

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