Thermoacoustic trap for medflies

The Mediterranean fruit fly (Ceratitis capitata) is a worldwide pest that infests hundreds of different fruits and other crops and had an estimated $1.5 billion impact during its last infestation in California. Traps play a big role in both detecting and eradicating an infestation in an area. To selectively target female flies, researchers in recent years have experimented with playing recorded broadcasts of buzzing males. The required outdoor sound levels, however, call for an amplifier–loudspeaker system that is large, expensive, and easily damaged in harsh weather. At last month’s meeting of the Acoustical Society of America, Steven Garrett and Kent Lau of the Pennsylvania State University unveiled a different method based on thermoacoustics (for a primer, see the article in Physics Today, July 1995, page 22 ). The characteristic sound of the male medfly’s wing-fanning vibrations has a dominant fundamental tone at about 350 Hz, a weak second harmonic, and amplitude modulations of roughly 25% at about 20 Hz. Garrett and Lau designed a trio of thermoacoustic sound generators to approximate the mating call. Similar to the one shown here, each uses an ordinary test tube that contains a ceramic heat-exchanging substrate and a heater coil. Two of the test tubes differ only slightly in length; combined, they produce a 20-Hz beating amplitude modulation around the desired fundamental tone. The third produces the higher pitched second harmonic. The researchers are now testing their cheap, weatherproof, and compact medfly mating-call mimic. (Abstract 1pAB11 at http://asa.aip.org/asasearch.html .)