INFERRING ACTIVITIES AND POPULATION DENSITY FROM
INCIDENTAL SOILBORNE SOUNDS OF WHITE GRUBS
M. Zhang1, R. L. Crocker2, R. Mankin3, K. Flanders4, R. Hickling5 & J. Brandhorst-Hubbard6.
1, 2Texas A&M Univ. Res. & Ext. Ctr., 17360 Coit Rd., Dallas, TX 75252-6599 USA; 3Ctr. for Med., Agric., and Vet. Entomol., USDA-ARS, 1700 S. W. 23rd Dr., Gainesville, FL 32608 USA; 4, 6The Alabama Coop. Ext. Serv., 208A Extension Hall, Auburn Univ., Auburn University, AL 36849-5629 USA; 5Nat. Ctr. for Physical Acoustics, Univ. of Mississippi, Coliseum Dr., University, MS 38677 USA.
Studies of soil arthropods often are hampered because the "black-box" nature of the soil environment generally necessitates destructive sampling. This is not compatible with repeated sampling, such as is needed in most long-term studies.
This research demonstrated that characteristic incidental sounds are produced in the audible frequency range by the larval stages (white grubs) of rhizophagous scarabaeids (Coleoptera). These sounds are classified as digging, positioning, feeding and internal body sounds, all of which can be separated by a practiced listener or by computerized analysis. There is some evidence of alarm sounds (Dr. Mankin).
Further, it utilized these sounds in making non-destructive measurements of the circadian activity patterns of Phyllophaga crinita larvae under constant and variable temperatures, plus the spatial distributions of P. congrua, P. crassissima, P. crinita and Cyclocephala lurida larvae in the soil variously under field, greenhouse, and laboratory conditions.
Single-microphone sound samples were compared with conventional soil-core sampling for measuring larval population densities in turfgrass.
Paired-microphone analyses made it possible to estimate the total number and approximate location of larvae in a sampled area.
Daily levels of activity increased with soil temperature under naturally fluctuating temperatures, but showed no pattern at a constant temperature.
Soil moisture influenced the sensitivity of measurements; sounds could be detected at greater distances in dry soil.
This approach promises to be of considerable value as a means of non-destructive sampling of these and other cryptic organisms.
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07/06/00 Richard Mankin