Laser vibrometry as a diagnostic tool for detecting wood-boring beetle larvae

Wood-boring insect pests, such as the invasive Asian longhorned beetle (ALB, Anoplophora glabripennis), are difficult to detect because larvae mine inside deciduous trees, logs or wood packing material. Currently, only visual survey methods are used, which are mostly unable to detect the presence of wood-boring insects. Bioacoustic detection, however, exploits sounds and vibrations produced by larvae during feeding and other movements inside the wood. Bioacoustic detection methods require mounting of the sensors, which can be complicated, time consuming and may even damage the surface of the tested material. Laser vibrometry avoids all these problems as vibrations produced by the larvae are detected via the laser beam. We used a portable digital laser vibrometer to detect the activity of mining ALB larvae within poplar logs. Three types of pulses were recorded: the broadband pulses lasting 1-2 ms were the most frequent, with frequency maxima between 8 and 13 kHz. Less frequent were the low and the high frequency pulses, covering frequency bands between 4 and 7, and 9 and 20 kHz, respectively. The signal-to-noise ratio across the whole frequency range (0-22 kHz) of the laser vibrometer was around 35 dB. We show that laser vibrometry can be successfully employed as a non-destructive diagnostic tool for detecting infestations by the wood-boring beetles.