SummaryA geophone system was used to monitor activity of subterranean termites and ants in a desert environment with low vibration noise. Examples of geophone signals were recorded from a colony of Rhytidoponera taurus (Forel), a colony of Camponotus denticulatus Kirby, and a termite colony (undetermined Drepanotermes sp.) under attack by ants from a nearby C. denticulatus colony. The geophone recordings were compared with signals recorded from accelerometers in a citrus grove containing Solenopsis invictaBuren workers. Several different types of insect-generated sounds were identified in the geophone recordings, including high-frequency ticks produced by R. taurus and C. denticulatus, and patterned bursts of head bangs produced by Drepanotermes. Although these sounds were weak, they had distinct frequencies and temporal patterns that facilitated their identification. Similarly, the S. invicta produced easily identified stridulations. Overall, both systems performed well in enabling identification of high-frequency or patterned sound pulses. The geophone was more sensitive than the accelerometer to low-frequency signals, but such signals were more difficult to distinguish from background noises than high-frequency pulses. The low cost of multiple-geophone systems may facilitate development of future applications for wide-area subterranean insect monitoring in quiet environments, particularly when the insects produce distinctive or patterned sound pulses.

Geophone Detection of Subterranean Termite and Ant ActivityRichard Mankin, USDA-ARS, CMAVE, 1700 SW 23rd Dr., Gainesville, FL 32608

MethodsThree different insect colonies were monitored with a geophone probe system (Fig. A) near the campus of the Arid Zone Research Institute in Alice Springs, Northern Territory, AU. The signal output was monitored by headphones and recorded on a portable Walkman model MZ-R700 (Sony Corp, New York, NY). S. invicta were monitored with an accelerometer system in an experimental field near Ft. Pierce FL (Fig. B).

Fig. B.. Accelerometer system for monitoring of S. invicta activity:

a. Bruel and Kjaeramplifier

b. Recorder withheadphones

c. Accelerometer

See Mankin et al. (2001)Fig. A. Geophone system (model GS-32CT, Geo Space LP, Houston, TX)

AcknowledgmentsAlan Andersen (CSIRO, Darwin) identified the ants and termites investigated at Alice Springs, AU. Everett Foreman and Betty Weaver (USDA-ARS Center for Medical, Agricultural, and Veterinary Entomology, Gainesville, FL) assisted with signal analysis. I thank Joe Benshemesh (Monash University, AU), the Arid Zone Research Institute, Alice Springs, AU, and Phil Taylor, (Macquarie University, Sydney AU) for research facilities support.

References

Mankin, R. W., S. L. Lapointe, and R. A. Franqui. 2001. Acoustic Surveying of Subterranean Insect Populations in Citrus Groves. J. Econ. Entomol. 94: 853-859.

Fig. 3. Examples of spectral profiles of Drepanotermeshead bangs, C. denticulatus and R. taurus ticks, and patterned (stridulation) and unpatterned (ticking) sounds by S. invicta. 0 8 16

Time (s)

.0 4.0 8.0 12.0 16.0 TIME (s)

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Drepanotermes head banging

C. denticulatus ticking

Fig. 4. Example of a period of concurrent head banging by Drepanotermes and ticking by C. denticulatus (head bangs and ticks were identified by least-squares matching of individual pulse spectra to profiles in Fig. 3).

ResultsExamples of signals recorded from R. taurus, C. denticulatus, Drepanotermes, and S. invicta colonies are shown in Fig. 1.

Time (s)

0 1.3 2.6

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1.1. Ticking by R. taurus

Geophonesensor

A

.00 0.55 1.10 1.66 2.21 TIME (s)

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1.3. Head banging by Drepanotermes

0 0.66 1.32 1.99 2.65 TIME (s)

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1.2. Ticking by C. denticulatus

1.4. Stridulating by S. invicta

Accelerometersensor

D1 D2

D3 D4

B

C

Fig. 1. Oscillograms of signals recorded from ant and termite mounds with a geophone (1.1-1.3) or an accelerometer (1.4). Insets show: two ticks recorded from mound with R. taurus (1.1.A); three ticks recorded from mound with C. denticulatus (1.2.B); 16 head bangs recorded from a mound of Drepanotermes under attack by C. denticulatus (1.3.C); and two series of slow and rapid stridulations (1.4.D1 and D2, respectively); and two isolated ticks (1.4.D3 - D4) recorded near a mound with S. invicta.

To enable visual identification of insect sounds, signals below 0.24 kHz were filtered in oscillograms 1.1-.3, and signals below 0.1 kHz in 1.4.

A) Accelerometer(w/quiet background)

B) Accelerometer(w/wind gusts)

C) Geophone

24.1

Frequency (kHz)

0.3 3.15 6.0

56.1

40.1

Vibr

atio

n Le

vel (

dB)

1.725 4.575

Fig. 2. Mean spectra of background noise in periods with no insect sounds. The geophone (2.C) and one accelerometer profile (2.A) were obtained during quiet periods with no listener-identified sounds. The second accelerometer profile (2.B) was obtained during a period that contained a wind burst.

Fig. 2 shows the levels of background noise present in the Australian and Florida field environments. The geophone is very sensitive to low-frequency signals, but background noise levels increase rapidly below 500 Hz and weak insect signals cannot be detected at these frequencies except in very quiet environments.

The most reliable procedure to distinguish low-level insect sounds from background noise involved identification of high-frequency ticks and head bangs (Fig. 3). Even these were sometimes difficult to identify except where they occurred in distinct patterns, e.g., the Drepanotermes head bangs (Fig. 1.3.C) and the S. invicta stridulations (Fig. 1.4.D1 and D2). Fig. 4 shows an oscillogram of a 16-s period where termite head bangs and ant ticks could be distinguished by spectral and temporal pattern differences.

c:74.8 dB d:60.6 dB e:64.5 dB

S. invictastridulating

C. denticulatusticking

Drepanotermes head banging

R. taurusticking

Rel

ativ

e Vi

brat

ion

Leve

l (dB

)

Frequency (kHz)

0.3 3.15 6.01.725 4.575

-2

-6

-10

-14

-18

-22

S. invictaticking