Bats and Pecans: A Growing Partnership

In southern Georgia, Research Associates testify to the benefits of bats…

Pecans are big business in the southern United States, but as with most commercial crops, insect pests can pose costly problems. Georgia produces more pecans than any other state, harvesting about $80 million worth annually. However, pecan pests cost Georgia growers $25 to $30 million per year. Most growers use conventional methods of pest control, relying heavily on chemical pesticides. Many farmers, however, are concerned about risks to personal safety and environmental health from pesticides, and are looking for alternatives. One Georgia family believes they’ve found a better, more natural way to fight pests in their pecan orchard.

Frank and Teresa Bibin own Pebble Hill Grove, a 27-acre (10.8 ha) organic pecan orchard in southern Georgia. Each year, more than 30% of their crop suffered damage from the hickory shuckworm (Cydia caryana), a major insect pest of pecan trees. Shuckworm moths lay eggs on developing pecans and the larvae burrow inside, destroying the nuts. Conventional growers typically spray pesticides six times per year just to control shuckworm outbreaks. To comply with organic standards, the Bibins sought another approach.

“When we decided to cut chemicals in our orchard, we realized that we were going to need some alternatives for insect control,” said Frank Bibin. By chance, they had picked up a BCI brochure at a state park and noticed that bats were helpful to farmers. They joined the North American Bat House Research Project and built their first nursery house in July 1996. They painted the bat house medium brown and mounted it in their orchard facing east. Bordered by woodlands, a wetland and multiple creeks and ponds, the orchard seemed like an ideal place to attract bats.

“We saw only an occasional bat before installing our first bat house,” remarked Bibin. Nevertheless, free-tailed bats (Tadarida brasiliensis) and evening bats (Nycticeius humeralis) began moving into the bat house in March 1998. By summer, 100 to 120 bats were present, which remained throughout the following winter. Not only did the Bibins see fewer moths that year, they also observed less damage from the shuckworm larvae than in years past. Were the bats really making that much of an impact? Or was there another explanation?

Excited by this apparent progress, the Bibins added a back-to-back pair of nursery houses beside the first house in March 1999. To test bats’ preferences, they painted the houses beige and oriented them east/west. Bats occupied the new houses within two weeks, and the population grew rapidly that summer. By September, the Bibins counted about 600 resident bats, with 400 to 500 using the new pair. On many evenings, they watched bats emerge and noticed that they returned several hours later to feed in the orchard. Their inspections revealed virtually no shuckworm larvae or damage in 1999.

The More The Merrier
The Bibins decided that winter to add larger homes to accommodate their growing colony. BCI assisted with two grants (see page 7) to help expand their experimentation. In March 2000, they built a back-to-back pair of 4-foot (1.2 m) “triple-wide” nursery houses [The Bat House Researcher, Spring 1998], oriented to face north/south. These large, dark brown houses attracted bats within three months, and have been their most successful to date. By July, 570 bats were using the north-facing house, and 880 occupied both houses by September. Their next addition, also in March, was an experimental 4-foot (1.2 m) house constructed by Maberry Centre Bat Homes of stucco-covered insulation board. This roost appeared to be too cool for maternity use, but it sheltered 300 to 350 bats occasionally from August to November. The Bibins were also granted a pair of BCI nursery houses and a Maberry plastic stucco house, all of which were occupied within one week of installation this past summer. In November 2000, the Bibins counted more than 1,700 bats in their bat houses. Having a variety of designs, exterior colors and orientations has allowed their colony to expand rapidly, and provides many options for bats when weather changes.

While no form of insect control is absolute, Bibin believes bats can play an integral role in pest reduction for pecan growers. “Before the bats arrived, if we left the light on in our pumphouse by the orchard at night, the room would fill with moths. Now, we see only a few moths,” said Bibin. Having found no shuckworm damage again in 2000, the Bibins are thrilled with their results, and are already building another pair of triple-wide nursery houses. Their problems with other pecan pests, including twig girdlers (Oncideres cingulata), stinkbugs (Nezara sp.) and fall webworms (Hyphantria cunea) have also decreased dramatically since attracting bats.

“We’ve spent far less on the bat houses than we would have spent on pesticides in just one year,” added Bibin. Considering that the annual cost of spraying for shuckworms alone would amount to $1,260 (a sizable investment for a small orchard), when multiplied over numerous pests the savings are significant. “I am convinced our decrease in damage from hickory shuckworms and other pests is because of the bats’ presence here. I think every grower needs to consider bats as an alternative to pesticides.

Research Associates Frank and Teresa Bibin attracted more than 1,700 free-tailed and evening bats to nine bat houses in their pecan orchard in southern Georgia. Since bats began moving in, damage from pecan pests has dropped dramatically.

In July, 570 bats pack into the north side of the Bibins’ triple-wide nursery pair. By September, 880 bats were using these houses. Note the small spacer blocks between each partition, which keep the long sheets of plywood from warping.