The Potential of Using Acoustical Emission to Detect Termites Within Wood

Acoustical emission (AE) equipment was used to detect drywood termites Incisitermes minor in ponderosa pine Pinus ponderosa blocks under laboratory conditions. Using a 60 kHz transducer, AE levels were recorded for 0, 5, 10, 15, and 20 termites per block. The association of AE and varying numbers of drywood termites best fit an exponential curve. These data suggest that the detection capabilities of AE increase with increasing numbers of termites. The implications of this finding to the potential use of AE in detecting termites under field conditions are discussed. In California, as many as 73 species of insects have been reported to cause damage to wooden structures (Ebeling 1975). Of these species, the subterranean termite Reticulitermes hesperus Banks and the drywood termite Incisitermes minor (Hagen) have had the greatest economic impact. Each year, more than 1.5 million inspection reports on termites and other wood-damaging pests are filed with the California Structural Pest Control Board (SPCB). Notices of Corrective Actions against these pests annually exceed 250,000, and the yearly costs of these inspections and control measures exceed $350 million (Brier and others 1988). In the past, control of termites within buildings relied heavily on the use of chlordane. However, because of problems involving environmental contamination and pesticide-related injuries, chlordane, along with many other pesticides, are no longer used or registered for control of wood-destroying insects. Since the discontinuance of the use of chlordane for subterranean termite control, recent reports reveal that termite control failures have increased as much as 30 percent (Katz 1989), and often result in additional callback treatments. As the number of callback treatments increases, there is concern that pesticide usage in urban areas, already more Presented at the Symposium on Current Research on Wood-Destroying Organisms and Future Prospects for Protecting Wood in Use, September 13, 1989, Bend, Oregon. Chancellor's Minority Postdoctoral Fellow, Department of Entomological Sciences, University of California, Berkeley, and Senior Research Specialist, Forest Products Laboratory, University of California, Berkeley. than 10 lb/acre, may also increase (National Academy of Sciences 1980). As a consequence, methods for reliable and accurate detection and control of termites are needed. Although new research shows promise for the development of nonchemical barriers, biological controls, attractants, and repellents for termites (Rust and others 1988), little has been done to improve inspections of structures. The use of electronic stethoscopes and dogs for detecting termites is gaining in popularity, though their utility has not yet been rigorously tested. Onsite visual inspection is still the dominant detection technique used by the industry. Unfortunately, visual inspection is highly subjective. Consequently, many of the 1,000 complaints filed each year with the California SPCB result in litigation. Acoustic emission (AE) (the generation, transmission, and reception of energy in the form of vibrational waves in matter) (Kinsler and others 1982) offers a potentially useful innovation for improving the detection of termites. The early applications of AE were for detecting defects and sounds emanating from metals (Dornfeld and Kannatey-Asibu 1980); however, new applications have been developed for machined wood (Lemaster and Dornfeld 1987), and sapwood trunk samples (Haack and others 1988). Although most AE studies are for stored grains and fruit-boring insects (Hansen and others 1988, Webb and others 1988), in Japan the Formosan subterranean termite (Coptotermes formosanus Shiraki) has also been studied (Fujii and others 1990). Because of the economic losses caused by termites in California, and the need for improved detection of wood-destroying insects, we initiated a pilot study on the use of AE for detecting termites. The insect species studied was the drywood termite Incisitermes minor. This species was chosen because of its importance as a wooddamaging pest and ease in laboratory rearing.