The battle commenced above the cotton field one hot February night. Cotton bollworm moths, whose larvae ravage cotton bolls, cut erratic paths across the dark sky. Bats of up to half a dozen species raced in hot pursuit, their echolocation calls beeping wildly on our bat detectors. And that aerial combat is exactly what I had come to Narrabri, in the cotton country of southeast Australia, to study.
Narrabri, at the edge of the outback in New South Wales, is studded with vast cotton fields interspersed with rolling hills. The Namoi River flows through Narrabri, providing water for farmers and others. Irrigation water is stored in lakes, which generally cover 3 to 5 acres and are full of old-growth eucalyptus trees. The areas around the lakes were teeming with birds – and, we soon discovered, with bats.
Our research, funded in part by Bat Conservation International, was to document the role of bats in controlling cotton pests. Our team included myself; Greg Richards, an Australian bat biologist; Monika Rhodes, a Ph.D. student from Australia’s Griffith University; John Westbrook, Research Leader at the U.S. Department of Agriculture’s Areawide Pest Management Research Unit in College Station, Texas; and Martin Dillon of the Australian Cotton Research Institute.
The major pest of cotton in Australia is the Old World cotton bollworm, a relative of the New World cotton bollworm that costs American farmers more than $1 billion a year. In North America, bats such as the Mexican free-tailed bats are prodigious predators of cotton bollworm moths and can sharply reduce the need for pesticides. We hoped to document a similar role of bats in Australia.
We quickly found that night skies above the fields were aswarm with flying bats and insects. We recorded six species of insectivorous bats, and there can be no doubt that they were hunting the insects in the cotton fields. When foraging bats appeared over a field, insects promptly took evasive action or fled. We observed moths spiraling into the cotton or suddenly increasing their flight speed.
We also demonstrated the importance of old-growth eucalyptus trees in maintaining the diversity and abundance of bats on cotton farms, and farmers are beginning to understand the economic value of conserving these trees to enhance bat activity for natural pest control.
RACHAEL LONG is a Farm Advisor with the University of California Cooperative Extension Service in Yolo County, California.