Putting bats to work

The impact of bats on crops like cotton and corn has been well studied and documented, said Mylea Bayless, conservation biologist for Bat Conservation International, a nonprofit organization based in Austin, Texas.

Mexican free-tailed bats are credited for saving Texas cotton and corn growers in an eight-county region nearly $750,000 each year from reduced pesticide applications and reduced crop damage, she said, citing a long-term research project by U.S. Department of Agriculture scientists.

Researchers are just beginning to study the benefits of having bats in orchards and vineyards, Bayless said. She shared information on bats and their habitat with growers at a fall workshop in The Dalles, Oregon.

The workshop was co-sponsored by the United States Department of Agriculture and the Wasco County Soil and Water Conservation District.

Using bats as an IPM strategy is a relatively new concept, both in the bat world and agriculture, explained Bayless. "We're only just beginning to understand the possibilities of how you can use bats in agriculture and tree fruit."

Insect diet

Bats come in many shapes and sizes, with appetites for a variety of food. But for agriculture, the micro-bat species are the ones of interest because of their vociferous hunger for insects.

In the past, much of the information about bats was anecdotal. With today's technology, scientists are now able to dissect bat guano and use DNA from insect fragments to learn specifically what bats eat.

On the West Coast, bats are primarily moth specialists, she said. Scientists have documented that bats eat a variety of tree fruit pests, including those in the Lepidoptera order, such as codling moth, as well as various beetles, true bugs (green and brown stinkbugs, leafhoppers, and cicadas), ants, wasps, bees, true flies, roaches, termites, mayflies, crickets, and even lacewings.

Tree fruit insects that scientists suspect are eaten by bats—though it's not yet confirmed—include obliquebanded leafroller, Pandemis leafroller, fruittree leafroller, and European leafroller. Researchers recently learned that bats consume the blue-green sharpshooter, a vector of Pierce's disease in grapes.

In California's Sacramento Valley, a University of California Cooperative Extension project analyzed the diets of little brown bats and found that moths made up about 35 percent of the bat droppings; mosquitoes 15 percent; beetles and plant bugs each 3 percent; and lacewings were present in small amounts.

UC data collected from pear orchards in Yolo County also found decreased codling moth numbers when orchards were located near bat roosts, she said. Codling moth damage was less than 5 percent when the orchard was located within a mile of a known bat roost, compared to 60 percent in an orchard located two miles away.

Bat species

While there are many bat species that inhabit the United States, not all utilize bat houses, as some prefer to live in caves, rock crevices, or in tree snags. However, Bayless identified six insect-eating species that use bat houses and are commonly found in Oregon's Wasco County.

The pallid bat is found in eastern Washington and Oregon and all of California, while the California bat and Yuma bat are found in Washington, Oregon, California, and a few other western states. The little brown bat and big brown bat are abundant throughout the United States; the long-legged bat is one of western America's most widely distributed species.

Profiles of 47 bat species living in the United States can be found on the Bat Conservation International's Web site. The site allows one to specify individual states to learn what bats are found there.

Attracting bats

How do you attract bats to your farm, orchard, or vineyard? Bats need the basics—food, water, and shelter. Bayless outlined steps growers can take to encourage bat roosts on their property:

1. Maintain insect diversity by using targeted insecticides instead of broad-spectrum insecticides (such as using GF-120 for cherry fruit fly instead of malathion). More bat foraging has been observed on organic farms.

2. Maintain habitat by providing vegetative corridors, protecting riparian areas, and maintaining native plant species in boundary areas.

3. Maintain complex vertical structures.

4. Provide accessible water. Bats must "drink on the wing" and need unobstructed space for a flight pattern. Long, narrow water troughs are better than round. Water must be constant with a stable water level. Don't let water supplies dry up.

5. Provide a wildlife escape structure in the water trough to prevent accidental drowning.

6. Leave tree snags as roosts in the orchard area.

7. Check abandoned buildings before they are torn down, as they may be the only structure in the area used by bat colonies.

8. Provide bat houses. A 12-year study found that bat houses located in orchards had the highest occupancy rate (83 percent) compared with bat houses placed near pastures, row crops, etc.

9. Place bat houses where they can provide a warm and stable temperature for bats to raise their young. Interior temperatures should be 80° to 100°F. Bats will occupy houses from April to October, then leave for winter hibernation. 

• More than 1,100 species of bats found worldwide; 47 species in the United States.
• One in every four mammal species is a bat.
• Bats eat different things, from nectar to insects to amphibians to fruit; 70 percent of all bat species eat insects.
• Bats pollinate 1,300 food crops and are the sole pollinators of the agave plant from which tequila is made.
• Bats are some of the slowest in terms of reprod­uction for mammals of their size. Most bats ­produce one pup per year.
• Bats use echolocation to find prey; some insects and moths can hear bat echolocations up to 100 feet away and avoid areas where bats are present. Even fake bat sounds can chase insects away.
• One little brown bat (Myotis lucifugus) can catch 1,200 mosquito-sized insects in one hour.
• A red bat (Lasionycteris noctivagans) that eats 100 moths may prevent the laying of eggs that could otherwise produce 25,000 new caterpillars to attack a crop.
  Information from Bat Conservation International.