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ABOUT BATS

There are more than 1,200 species of bats found worldwide. Approximately 70% are insect eaters. These bats consume millions of pounds of insects per night, many of which are agricultural pests. The positive benefit to farmers and gardeners is enormous.


There are 47 species of bats found in the United States, and at least 15 have been documented to use bat houses. Of these, there are several species that form colonies large enough to control insects effectively in a farm or gardening situation, including the Brazilian free-tailed bat, little brown bat, big brown bat and the evening bat.


Our primary focus at Pebble Hill Grove is attracting Brazilian free-tailed bats, which occur across the southern United States. Their tendency to form large colonies and high success rates with artificial roosts makes them ideal candidates for integrated pest management programs.


The recent development of DNA testing methods has proven to be the most powerful tool in determining the diet of bats. DNA fragments of corn earworm moth, tobacco budworm moth, cabbage looper moth and fall armyworm moth have been identified in the guano of the Brazilian free-tailed bat (Lee and McCracken, 2005). The larvae of these moths are some of the most destructive agricultural pests in the United States. The USDA estimates the corn earworm and tobacco budworm alone cause over a billion dollars in crop losses per year.


Our farm is certified organic, but bats are also useful in conventional farming operations. However, bat roosts must always be protected from pesticide spray drift. This may involve setting up roosts adjacent to fields, or mounting roosts inside a barn or shelter.


We put up our first bat roost in 1996 as a possible means of insect control in our 27 acre pecan grove in Brooks County, GA. We now have seven double roosts and two single roosts spaced within our grove. Our seasonal peak population is about 3,500 Brazilian free-tailed bats with several hundred evening bats. Multiple bat species often roost together.


We have seen large reductions in pecan damage from pecan nut casebearer, fall webworm, walnut caterpillar, stinkbug, twig girdler and periodic reductions in hickory shuck worm. Evidence suggests that the closer the roosts are to the crop, the greater the insect control. We believe bats are effective against pest insects in two ways:
1.    By directly consuming the pest insects.
2.    By causing pest insects to avoid areas of high bat activity, such as near roost sites.


The bats in our grove typically depart to hunt immediately after emerging from their roosts at twilight, returning around 10 pm. They alternate between resting in their roosts and flying methodically within a few hundred feet of their roosts. Using bat detectors during this time reveals a large number of   feeding buzzes, which indicates an increase in echolocation frequency as the bats close in on prey. They will do this for two to three hours and then leave on another hunt. Based on these findings, bats are hunting within our pecan grove about 50% of total nighttime hours.


Dr. Jim Dutcher, an entomologist with the University of Georgia experiment station in Tifton, set up light traps in our grove during the growing season of 2006 to sample for general moth activity and found low levels compared to other sites in Georgia. His tree by tree assessment of our orchard conducted in September 2006 found low incidence of fall webworm damage and no walnut caterpillar damage. Final pecan assessment at harvest time revealed only hickory shuckworm damage.


The size of prey determines how often an insect is included in a bat’s diet. If larger, more preferred prey items are available as in periods of peak emergence, smaller prey may be ignored. A good example is the hickory shuckworm moth, which is the smallest moth pest in our grove, with a wingspan of about 3/8- inch. The DNA of this moth has been verified in guano samples taken from bat houses in our grove (Veronica Brown, 2008).  Control of this moth in our grove is periodic. The larger pecan nut casebearer moth (½-to ¾- inch wingspan) has also been verified by DNA analysis in our guano samples (Veronica Brown, 2008).  Peak emergence levels in our orchard in May are consistently lower than other sites sampled. The percentage of nut damage from casebearers at harvest is always insignificant. This may indicate that  predation is more consistent. Infestation levels of fall webworm moth with a wingspan of 1 inch and walnut caterpillar moth with a wingspan of 1 ½ to 2 inches are also consistently low.   


Some insects that are normally considered to be diurnal may have partial or periodic nocturnal activity. Research indicates that some insects mate during the hour before dawn, a peak bat feeding period. Stinkbugs, which are diurnal and are major agricultural pests, have been verified through DNA as well as microscopic analysis in guano samples taken from under bat houses in our grove (Veronica Brown, 2008).


A University of Tennessee study conducted in 2006 found corn earworm moth DNA in guano samples taken from captured bats in our grove (Dr. Gary McCracken, 2006) , proving that the bats are hunting around the other farms in the area. The corn earworm also known as the cotton bollworm, is not a pecan pest but is destructive to most other crops in our area, including cotton. We wanted to find out how well the bats could control corn earworm moth on sweet corn planted on our farm, so we applied for and received a SARE (Sustainable Agriculture Research and Education) grant. The following is a summary taken from our final report:

CONTROL OF CORN EARWORM MOTH USING BRAZILIAN FREE-TAILED BATS

FS07-212                                                                                                                                       
Frank and Teresa Bibin- Pebble Hill Grove
9047 Moultrie Hwy.
Quitman, GA 31643
E-mail: This e-mail address is being protected from spambots. You need JavaScript enabled to view it

Cooperators:
•    James D. Dutcher, Ph.D. - UGA; Entomology
•    Mylea Bayless, M.S.  - Bat Conservation International

The purpose of our project was to determine if Brazilian free-tailed bat predation can decrease corn earworm infestation levels in sweet corn.

Our method involved planting a sweet corn plot 70 ft X 70 ft in size in close proximity to established free-tailed bat colonies. The corn was planted in early, middle, and late stages with a control plot corresponding with the early stage corn. The control plot of corn was located at the UGA experiment station in Tifton, about 100 miles north of our farm. Pheromone and light traps were used to sample adult corn earworm moth levels.

Results indicated early sweet corn (phase 1) averaged a 26% corn earworm infestation rate, while the control plot averaged a 53% infestation rate. Corn earworm infestation rates in the middle corn (phase 2) and late corn (phase 3) increased successively.

Final assessment of our project indicated that bat predation is an effective control of corn earworm moths in early sweet corn, but not in late season sweet corn  To read the complete report, visit the SARE website: www.southernsare.org. Under Project Reports, click on the Search the Database link. In the search string field, type in our project number, FS07-212 (2007 abstract).
Free-tailed bats, like other bat species, eat about one- half their body weight in insects per night. Lactating females eat almost two-thirds of their body weight per night, equaling about 15-20 corn earworm moths. The free-tailed bats roosting in our grove eat about fifty pounds of insects per night.

An added benefit of on site bat colonies is the guano that collects under the houses. Rich in nitrogen, phosphorus, potassium and calcium, it is an excellent fertilizer in its raw form. We make a guano extract using a natural fermentation process. Lab analysis revealed moderately high levels of N-P-K and calcium. The extract can be diluted to a ratio of 1 to 100 with water and applied through a sprayer or used as a ground drench. We are usually able to collect about 400 to 500 lbs. of guano a year.

Free-tailed bats, big brown bats, little brown bats and evening bats often roost in older building, bridges and other man-made structures. Thousands may live in the historic districts of towns and cities. With the loss of natural habitats as well as artificial roosts due to evictions and deterioration of older buildings, populations of these bats are declining. Through new techniques in DNA analysis and further research, county extension agents and farmers can come to view bats as a valuable resource. Roosts erected on farms will greatly improve insect control and give bats a preferable alternative to roosting in our homes and buildings. For further information about bats, visit Bat Conservation International: www.batcon.org.

WHITE- NOSE SYNDROME

White -Nose syndrome (WNS) is a fatal disease affecting many of the hibernating bat species in the United States and Canada. The disease appears to be causes by a fungus called Geomyces Destructans. The fungus itself does not kill the bats directly but interrupts their hibernation cycle by causing them to repeatedly awaken. Winter fat reserves are used up and bats either starve or freeze.

The fungus grows on the bats during hibernation when metabolic rates and immune response are lowered. The temperature and humidity levels in the hibernation caves and mines are favorable for growth of the fungus. It is estimated that well over one million bats in eastern North America have already died, and the disease continues to spread westward each year.

The bright spot in this catastrophe is that the Brazilian free-tailed bat and the evening bat do not hibernate and do not appear to be affected in the same way as hibernating species. Even if WNS can be passed on to the free-tailed bat, it is unlikely to become more than a nuisance infection. So far, no evidence has been found of WNS in the free-tailed bat population. For more information on WNS, visit the U.S. Fish and Wildlife Service Website: www.fws.gov/whitenosesyndrome.  For more information on bats and caves, visit: Bat Conservation International: www.batcon.org  and the National Speleological Society: www.caves.org.

 

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