A Closer Look into Drywood Termite Detection Using Microwaves

Published February 26, 2019

Figure 1. Western drywood termite (*Incisitermes minor*) workers (pseudergates) and soldiers.

The western drywood termite (Incisitermes minor) (see Figure 1) is an important structural pest, especially in California and Arizona, causing an estimated damage of $250 million annually (Cabrera and Scheffrahn 2017). These termites are hard to detect in structures due to their very cryptic nature. Most drywood termites live entirely within wood and rarely leave their galleries. The only time people notice their presence is when alates (winged termites) swarm, when fecal pellets are seen in or around the structure, or when inspections reveal subsurface tunnels within structural wood. Among these signs, only the presence of live alates is proof of an active infestation (the other two may only indicate old infestations).

Drywood termite control methods in structures are generally divided into local and whole-structure treatments. The efficacy of any local treatment is dependent on the accurate detection of active infestation sites and, sometimes, access to subsurface galleries. Therefore, researchers and pest management professionals have sought non-destructive methods and tools to pinpoint active infestations within structural wood members. Several different methods — such as x-ray, acoustic emission, low-energy microwaves, canine detection and infrared cameras — have been tested by researchers for their efficacy in detecting drywood termites. Some of these methods are currently utilized by PMPs, but based on published research, there is no “silver bullet” when it comes to drywood termite detection. However, when used properly, any of these methods can partly reveal infestations inside a structure, helping PMPs to better control drywood termites.

Figure 2. A screenshot from the Termatrac software application (Ver. 3.19) showing “Radar line graph” (a), “Radar bar graph” (b), “Shake/Accelerometer line graph” (c), “Shake/Accelerometer bar graph” (d) and “Gain” control (e). *Source: Taravati (2018)*

One relatively recent termite detection technology on the market uses radar (low-energy microwaves) to detect motion; it is commercially known as Termatrac. The first model, Termatrac T1r, came out in 1999. It was eventually followed in 2010 by the second and latest model, the Termatrac T3i (Taravati 2018). Termatrac T3i is different from acoustic emission devices, which detect sound created by termites biting and nibbling on wood (Scheffrahn et al. 1993). In addition to detecting motion within wood, Termatrac T3i can also detect moisture and measure surface temperatures, using two other sensors. One challenge when using termite detection devices is interpretation of their output. In this case, Termatrac’s radar sensor provides output in the form of a line graph as well as a bar graph (see Figure 2).

Like acoustic emission devices, Termatrac can pick up signals from non-target sources — such as moving vehicles, people, pets, other insects (e.g., ants), water in pipes, and strong shaking or vibrations. All of these may produce a false positive result, meaning the device shows an indication of live termites when no termites are actually present. Also, the output signal weakens as the depth of detection (distance from the sensor to a termite) increases; this may produce a false negative result (not detecting termites when they are present). Therefore, PMPs must be careful when interpreting Termtrac’s output graphs. In order to evaluate the termite detection efficacy of Termatrac T3i and to improve interpretation of its output, I conducted field and laboratory studies in Southern California. A technical account of the laboratory work has already been published (Taravati 2018,).

FIELD STUDY. Termatrac T3i was tested in five different single-family houses (see Table 1) in Southern California, most of which had confirmed drywood termite infestations in the past. Elements of structures inspected included interior and exterior walls, baseboards, wood fences, and frames of windows and doors. The device was tested using several operational methods:

Held in hand, radar surface flush against the inspection site (structural element such as a wall that is suspected to harbor termites) (see Figure 3a).
Mounted on a tripod, radar surface flush against the inspection site (see Figure 3b).
Resting flat on a horizontal surface, radar surface flush against the inspection site (see Figure 3c).
Radar surface at 45-degree angle to the inspection site using the flip stand (back flap) or on a tripod (see Figure 3d).

Figure 3. Different positions/configurations for using Termatrac T3i as evaluated during the field study.

During field inspections, residents were asked to minimize noise and movement (of both people and pets) in and around the house. Careful observations were made on the position of the Termatrac device, fluctuations in output signal, and the presence of any movement in front of, at the sides of, behind the device and on the other side of the wall.

RESULTS. Several sources of interference, leading to false positive results, were identified during this study. These included:

Operator’s hand shaking when using the device while it is held in the hand(s). Author’s note: I could not reliably use Termatrac as a hand-held device. Even the slightest hand shaking produced detectable signals, especially at settings of increased sensitivity (high “gain”).
General operator movement during readings. Even the slightest body movement of the operator can produce detectable signals. At higher gain settings, this is true even when the device is placed on a tripod and when the operator stands behind the device.
Movement of people or pets adjacent to or on the other side of the inspection site. Termatrac easily can pick up movement, at the sides of the device and even behind the device head (radar surface).
Movement of vehicles on the street behind the inspection site.
Movement of plants (branches), especially due to wind, behind or against exterior walls being inspected (see Figure 4). The false signal produced can be weak to very strong, depending on wall thickness, wind intensity and plant structure.
Movement of airborne debris, such as fallen leaves in the wind, behind exterior walls being inspected.
Movement of wood fences swaying in the wind (see Figure 5). Even fences that seem very stable can produce detectable signals with the slightest breeze.
Movement of water within pipes in the inspection site. Water moving in pipes can generate a strong signal. False positive results were recorded when inspecting walls near bathtubs in bathrooms.

Figure 4. Plants behind walls can move with the wind, potentially producing false positive results. Figures 5a and 5b. Wood fences can sway with even the slightest breeze, potentially producing false positive results. Figure 6. Experimental setup in the laboratory, showing the Termatrac device, a painted section of drywall, wooden “studs,” and a vial containing sand and a Hexbug Nano taped to a coffee container partially filled with sand.

In general, using the Termatrac’s radar surface at 45 degrees to the inspection surface resulted in more interference as compared to when the radar’s surface was flush against the wall. Surprisingly, Termatrac did not pick up vibrations from heavy machinery working loudly nearby. This makes Termatrac an available inspection tool, even for operators in noisy locations.

LABORATORY STUDY. Since drywood termite detection attempts are difficult to evaluate in the field without using destructive methods (removal and cutting of wood members to confirm infestations), laboratory experiments were necessary to evaluate the efficacy of Termatrac. The objective of these experiments was to find a practical way to visually interpret Termatrac’s signal, helping PMPs to use the technology with more confidence and more accuracy. These experiments also aimed to measure the effects of wood type, termite density and detection depth on signal strength.

A drywall model (see Figure 6) was constructed using gypsum patching panel drywall (The Sheetrock Brand) painted with white acrylic paint and primer (Behr Premium Plus Ultra Stain-blocking Paint & Primer) and a standard 2 by 4 wooden wall stud. Two wood types were included in this study:

Prime whitewood hemlock or fir (HEM-FIR), kiln-dried (KD) and heat-treated (HT) structural stud — Stimson Lumber Company, Portland, Ore.
Prime green Douglas fir, surfaced-green (S-GRN) structural stud — Stimson Lumber Company, Portland, Ore.

Each stud was cut into 1-, 3- and 5-cm pieces (see Figure 7) using a power saw. Detection experiments were then conducted in the laboratory using two different targets:

Experiment I: A Hexbug Nano (Innovation First Labs) micro-robot as a source of movement/vibration.
Experiment II: Live Western drywood termite workers (pseudergates).

Signal strength was measured when using different combinations of wood type, wood thickness and presence of drywall. In experiment I, the source of movement was a single Hexbug Nano micro-robot buried halfway into sand in a plastic vial. The sand was used to limit the movement of Hexbug in the vial, decreasing signal intensity to be more similar to that produced by real drywood termites.

Figure 7. Wood sections of different thicknesses, cut from structural “studs,” to be used in laboratory experiments.

In experiment II, vials contained either one or ten live drywood termites. As in experiment I, different combinations of wall layers were used between the Termatrac device and the target. Both experiments were replicated 10 times. Hexbugs or live termites were placed on one side of the model drywall and the Termatrac device was placed on the opposite side. The device was turned on and connected via Bluetooth technology to a Samsung Galaxy Grand Prime smartphone running Termatrac software application (Ver. 3.19). The “radar” mode was selected and 15-20 seconds was given for the device to self-calibrate before reading the signal (this protocol was according to the manufacturer instructions). After self-calibration, a screenshot (see Figure 2) was taken of the device output; this image was later transferred to a PC for analysis. To be able to measure and compare Termatrac’s signal quantitatively, line graphs from the screen shots were processed in Adobe Photoshop CC (2017) to approximate the area under the curve, measured as the number of pixels squared.

RESULTS. Experiment I used two wood types and several different detection depths. Wood type did not have a significant effect on signal strength while detection depth certainly did. Signal strength decreased as the number and thickness of “wall” layers increased. The results from experiment II showed that termite density (either one or ten termites per vial) did not significantly affect signal strength. On the other hand, as with experiment I, “wall” layers significantly affected signal strength. Experiment II showed that Termatrac is able to detect a single drywood termite, confirming the manufacturer’s claim. I was able to detect a single drywood termite even when it was behind drywall and a 5-cm piece of wood (total “wall” thickness: 6.3 cm).

Termatrac screenshots can be used as general references for typical device signals in the presence of drywood termites in structures. Shapes and heights in the line graph output vary greatly between replicates, making it difficult to generalize the output signal. Also, weak signals coming from termites deep inside the wood makes it hard to distinguish between live termites and signal interference from other sources. Sometimes, this can be overcome by reducing the gain. However, lower sensitivity associated with lower gain values may reduce the detection range or overall ability within a structure.

PMP TIPS FOR USE. To conclude, laboratory results when using Termatrac T3i with simulated “wall” showed potential promise for drywood termite detection. Nevertheless, PMPs should bear in mind that real field situations will always be different from the laboratory settings used. The following suggestions are provided to help PMPs use Termatrac more efficiently and accurately:

Avoid getting false positive results by reducing movements around the device and by checking your surroundings before using Termatrac.
Always check the other side of the wall for any moving things (plants moving with wind, animals, vehicles, etc.) before using Termatrac.
Use a tripod to secure the device before reading the signal to reduce shaking.
Stand right behind the device and stand still when reading Termatrac’s signal to avoid adding noise and getting a false positive result.
Avoid inspecting non-fixed objects such as outdoor wood fences (which easily sway).
Consider using a stud finder to locate wooden studs behind wall coverings instead of blindly scanning wall surfaces. This will save you a lot of time and will help you to avoid inspecting portions of the wall that do not have underlying wooden studs. Remember that stud finders use the very same technology (microwaves) to detect studs and other objects and may not always be accurate.
Inspections of window and door frames, kitchen countertops, wood floors and other wood members that are not hidden behind walls will result in the most accurate detections of infestations. So whenever in doubt, focus on these areas when inspecting with Termatrac.
Drywood termite activity changes throughout the day and may change suddenly after physical impacts or disturbances. When you think you have detected termites, re-inspect wood members or wall sections with Termatrac after a few minutes to confirm the infestation. Signal strength can change during different signal readings of the same infested wood member. If termites are present but not moving, you can get a false negative result, which can be as bad or worse than a false positive result.
Keep in mind that higher densities of termites may not necessarily produce stronger signals (higher peaks in the line graph output).

The author is an urban IPM adviser at the University of California Cooperative Extension — Los Angeles County office.

Author’s Acknowledgments/Note: I would like to thank Dr. Andrew Sutherland; Dr. Darren Haver; Termatrac’s Rick Wakenigg, Michelle Lutz and Victoria Johnston; Dr. Mike Rust; Dr. Dong-Hwan Choe; Dr. Rachel Surls and Valerie Borel; all the UCCE-Los Angeles Master Gardeners who allowed me to use their property for testing. This project was made possible by funding provided by the statewide UC-Integrated Pest Management Program (UC-IPM) program.