ECOLOGY AND BEHAVIOR Acoustic Detection of Oryctes rhinoceros (Coleoptera: Scarabaeidae: Dynastinae) and Nasutitermes luzonicus (Isoptera: Termitidae) in Palm Trees in Urban Guam 1 2 R. W. MANKIN AND A. MOORE J. Econ. Entomol. 103(4): 1135Ð1143 (2010); DOI: 10.1603/EC09214 ABSTRACT Adult and larval Oryctes rhinoceros (L.) (Coleoptera: Scarabaeidae: Dynastinae) were acoustically detected in live and dead palm trees and logs in recently invaded areas of Guam, along with Nasutitermes luzonicus Oshima (Isoptera: Termitidae), and other small, sound-pro- ducing invertebrates and invertebrates. The low-frequency, long-duration sound-impulse trains produced by large, active O. rhinoceros and the higher frequency, shorter impulse trains produced by feeding N. luzonicus had distinctive spectral and temporal patterns that facilitated their identiÞcation and discrimination from background noise, as well as from roaches, earwigs, and other small sound-producing organisms present in the trees and logs The distinctiveness of the O. rhinoceros sounds enables current usage of acoustic detection as a tactic in GuamÕs ongoing O. rhinoceros eradication program. KEY WORDS invasive species, acoustic detection, eradication Adult Oryctes rhinoceros (L.) Coleoptera: Scar- Spot treatment of palms and breeding sites has been abaeidae: Dynastinae) bore into and feed inside conducted with conventional and injectable insecti- emerging fronds at the crowns of coconut (Cocos cides (Smith and Moore 2008). nucifera L.) and other palm trees in Southeast Asia Visual inspection of frond and trunk damage is the and tropical PaciÞc islands, causing extensive dam- most commonly used method of detecting O. rhi- age (Gressitt 1953, Hinckley 1973, Bedford 1980, noceros adults; however, infestations cannot be de- Jackson and Klein 2006). Frequent attacks by sev- tected easily from the ground until well after sig- eral adults may kill a tree. Larvae feed inside rotting niÞcant damage has occurred. Because adults, logs of palms killed by adults or by high winds from larvae, and pupae are known to produce audible typhoons that pass through the tropical PaciÞc an- sounds (Gressitt 1953, Mini and Prabhu 1990), it was nually. Introductions of O. rhinoceros into the Palau of interest to determine whether adults feeding and Islands and other originally uninfested regions have moving in the crowns of live trees and larvae feeding resulted in considerable economic harm to coconut in standing, dead trunks can be detected by acoustic palm plantations (Gressitt 1953). methods (e.g., Mankin et al. 2000, 2002, 2008a,b). O. rhinoceros was unknown in Guam until 2007 Previous experience with detection of insect sounds (Smith and Moore 2008), and due to the considerable in trees (e.g., Mankin et al. 2008b) suggested that a potential for economic damage, the Tumon Bay hotel combination of spectral and temporal pattern fea- district was quarantined a few days after an adult female was discovered in the area. Mass trapping was tures of detected sounds could be used to distin- initiated with commercially available aggregation guish O. rhinoceros signals from nontarget signals in pheromone oryctalure (ethyl 4-methyloctanoate) the noisy urban areas of the quarantine zone. A large (Hallett et al. 1995, Ramle et al. 2005), and a program insect like O. rhinoceros might perform boring and was established to remove or treat rotting coconut logs feeding activities that produced louder and longer and other potential breeding and larval feeding sites. sounds than those produced by other small insects that also were associated with palm trees, including Pycnoscelus surinamensis (L.) (Blattodea: Blaberi- The use of trade, Þrm, or corporation names in this publication does dae), Brontispa palauensis (Esaki & Chujo) (Co- not constitute an ofÞcial endorsement or approval by the United States Department of Agriculture, Agricultural Research Service of leoptera: Chrysomelidae) (Muniappan 2002), Che- any product or service to the exclusion of others that may be suitable. lisoches morio (F.) (Dermaptera: Chelisochidae), 1 Corresponding author: USDAÐARS, Center for Medical, Agricul- and tenebrionids. Here, we report on a study con- tural, and Veterinary Entomology, Gainesville, FL 32608 (e-mail: ducted to determine the feasibility of incorporating [email protected]). 2 College of Natural and Applied Sciences, University of Guam, acoustic detection methods into the ongoing pro- Mangilao, Guam 96923. gram to isolate and eradicate breeding populations. 1136 JOURNAL OF ECONOMIC ENTOMOLOGY Vol. 103, no. 4 Materials and Methods signal below 200 Hz was background noise and no important signal features were observed Ͼ5 kHz, the Records were collected over an 11-d period from 11 signals were band-pass Þltered between 0.2 and 5 kHz live palm trees, six dead palm trees, seven logs, and Þve to facilitate subsequent analyses. In the initial screen- stumps that were easily accessible and available for ings, we conÞrmed the presence of groups (trains) of (destructive) inspection at several different locations discrete, 3Ð10-ms impulses separated by intervals in the Tumon Bay hotel district quarantine zone. Ex- Ͻ250 ms. Such trains had appeared frequently in re- ternal veriÞcation of the insects present at each site Ϸ cordings at sites where insects were recovered in pre- was performed within 24 h after recording by felling vious studies (Zhang et al. 2003a,b; Mankin et al. a tree if it was standing, splitting open the trunk, log, 2008a,b). Trains containing 15 or more impulses were or stump tissue with axes and knives, and sorting a focus of analysis because they often were identiÞed through the separated pieces. The surveyed locations as insect sounds in playbacks of recordings from in- included the grounds of a hospital, a hotel, a retire- fested sites, but trains containing only small numbers ment complex, a shopping center, and three houses, as of impulses, as well as signals without any 3Ð10-ms well as a rubbish pile. Although O. rhinoceros were impulses, usually were interpreted as background known to be present in the quarantine zone, none of noise (Mankin et al. 2008b). the individual trees, logs, or stumps in the Þeld study The impulses and impulse trains detected in the had been inspected previously. Temperatures were recordings were analyzed with customized software, Ϸ Њ 28Ð31 C at the times of recording. DAVIS (Digitize, Analyze, and Visualize Insect To gain additional knowledge of the characteristics Sounds, Mankin 1994, Mankin et al. 2000), which dis- of signals produced by larval and adult O. rhinoceros, carded long-duration, low frequency background records were collected also from separate groups of O. noise (Mankin et al. 2007, 2008a,b) and then compa- rhinoceros larvae and adults maintained in a rearing red the spectrum of a 512-point time-slice centered facility at the University of Guam. These beetles were around the peak of each impulse against averaged held in 30- by 24- by 24-cm plastic rearing cages con- spectra (spectral proÞles) of independently veriÞed taining pieces of sugar cane and palm trunk. The lab- insect-produced signals and impulsive, tree bending- oratory studies are described separately from the Þeld grinding noises (see next section). The spectral com- studies in the last section of the Results because the parisons were performed after normalizing the accel- spectral characteristics of the sounds depend strongly eration (Mankin and Benshemesh 2006). on the substrate in which insects are moving and Insect and Background-Noise Spectral Profiles. feeding (Mankin et al. 2008). Spectral proÞles (Mankin 1994, Mankin et al. 2000) Acoustic Sensors and Recording Procedures. Signals were constructed from background noise impulse were collected from accelerometers attached to trains and four types of insect sound impulse trains, charge ampliÞers (Mankin et al. 2000, 2001, 2002). The two of which were produced by the primary targets, ampliÞed signals were saved on a dual-channel, digital adult and larval O. rhinoceros. An adult O. rhinoceros audio recorder sampling at 44.1 kHz (24 bits). In proÞle, rhino_a, was averaged from 33 consecutive recordings at a survey location, the accelerometers impulse trains collected at a live palm where an adult were attached magnetically to 30-cm-long spikes, in- was recovered, and a larval proÞle, rhino_l, from 35 serted into the wood a few minutes before recording. consecutive impulse trains collected at the log where In laboratory recordings of O. rhinoceros held in rear- 72 larvae were recovered. One of two nontarget-insect ing containers, the accelerometer was attached to the proÞles, termite, was constructed from 233 consecu- rearing container or to a small nail inserted into one tive impulse trains produced in a dead palm where of the palm pieces on which the insects were feeding. only Nasutitermes luzonicus Oshima (Snyder and Listeners (see Acknowledgments) could monitor the Francia 1960, Su and Scheffrahn 1998) were recov- signals using headphones attached to the recorder, ered, and the second from 45 consecutive impulse thereby avoiding levels of wind or street noise high trains produced in a live palm where two nontarget enough to mask insect sounds. Wind noise caused species, P. surinamensis and B. palauensis, were the delays in 20Ð30% of the recording trials, but in all cases only organisms recovered. A background noise proÞle there were sufÞcient intervals of reduced background was generated as a spectral average of wind-induced noise to permit useful recordings of insect sounds for tapping and trunk bending and grinding that produce periods of 45 s or longer. In the absence of background short, broadband sound impulses (e.g., Fukuda et al. interference, records were collected for 180 s or 2007). A series of 38 consecutive impulse trains re- longer. Dual-channel recordings from two accelerom- corded at an uninfested palm were used in construct- eters were obtained from several Þeld sites, in which ing this proÞle. cases the channel with the greatest clarity was se- After the proÞles mentioned above were con- lected for analysis. structed from individual Þles, the complete set of Þles Digital Signal Processing and Classification.