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Eavesdropping on Insects in Soil and Plants

By Jesús García
January 5, 2001

Agricultural Research Service scientists and colleagues have adapted acoustic techniques--commonly used by engineers to predict mechanical failures--to detect insects hidden in soil and the interior of plants.

Researchers at ARS laboratories in Gainesville and Ft. Pierce, Fla., and Corvallis, Ore., and colleagues at Auburn University, University of Florida and Montana State University have collaborated on the development of an acoustic technique that uses sensitive instruments like accelerometers, soil-probe electret microphones and piezoelectric disks to pinpoint insect locations. These sensors convert vibrations into electrical signals.

Because insect pests often reside within plant structures and in soil, they can be hard to detect. As a result, field searches often include a visual inspection followed by digging, removal of the root mass or flushing with water, all of which are damaging to the plant. So researchers have been trying to find a less destructive way of determining the incidence of insect infestations.

The scientists conducted tests using a variety of insects and soil conditions in Florida, Oregon and Puerto Rico. The kinds of insects used--like the wheat stem sawfly and weevils that attack the roots of orange trees and ornamental plants--were chosen for their economic importance and variations in size.

The portable acoustic sensors were found to detect insects within 180 seconds over distances of 10-30 cm, depending on the composition of the soil and peak frequencies of the sound pulses. Those sound pulses were then averaged to create profiles for each insect.

Since background noises such as wind, airplanes and motor vehicles often interfere with researchers’ ability to accurately determine the presence of an insect, acoustic profiles were developed for them as well. Those profiles were then used to conduct tests that compared acoustically predicted infestations with insects found in the soil at recording sites. Under laboratory or ideal field conditions--with low levels of low-frequency background noise--insects within 30 cm were detected 100 percent of the time. Under adverse conditions in the field, the technique was 75 percent reliable.

This inexpensive and nondestructive pest-monitoring method may prove useful to growers intent on using integrated pest management systems to lessen the impact of a variety of insect pests on farm productivity. ARS is the U.S. Department of Agriculture’s chief scientific research agency.

Scientific contact: Richard W. Mankin, ARS Center for Medical, Agricultural, and Veterinary Entomology, Gainesville, Fla., phone (352) 374-5774, fax (352) 374-5781,