## 1 Introduction  
Termites consume wood members of structures and are one of the most destructive insects in households, reservoirs, and agriculture in terms of damage and control costs. The global economic loss due to damage and control mainly caused by termites was more than US$40 billion according to an estimate with 2010 data, and subterranean termites contribute 80% of the total damages [1; 2; 3]. Methods to control termites include applying liquid insecticide in the soil surrounding structures to form a uniform and continuous barrier, using slow-acting termiticide powders for the remedial control [4], preparing physical barriers, such as high-grade stainless-steel mesh to prevent termite invasion [3], or utilizing excavation strategies to destroy termite nests [5]. Monitoring and locating the termites is one of the most important processes for these strategies to prevent termite infestation. Termite bait stations can be used for monitoring termite activity and for pest management. Bait stations containing corrugated board or other wood materials are also applied to attract termites, and then termiticides can be applied. Bait stations have become one of termite management methods [6; 7; 8]. Unlike traditional liquid insecticides treatment, the adoption of monitoring-baiting stations can reduce termiticide use significantly. Monitoring-baiting stations have been widely used for integrated termite management, especially for termite remedial control [3; 9; 10]. These stations rely on manual routine inspection to determine the presence of worker termites in or around the wood bait inside the station. However, inspection is labor intensive and may disturb termite activity and give inaccurate information. Monitoring termite activities, especially remote monitoring, plays a very important role in termite control. Therefore, there is a need for a semi-automatic or fully automatic monitoring system instead of manual baiting stations to reduce the labor and cost. A semi-automatic or fully automatic system that has non-invasive monitoring features would provide useful information on termite activity without manual inspection and could save time and labor especially when inspecting bait stations. To date, several automatic monitoring devices based on various sensors are available for termite management. The automatic monitoring devices available include those based on an acoustic emission (AE) sensor [11; 12; 13; 14; 15], a wireless smart probe [16], a silver particle circuit painted on a wood piece or polyethylene sheet in the termite monitoring-baiting station [17; 18], odor detection [19], temperature, gas, and relative humidity detection [20], infrared cameras [21], computer tomography and endoscopy [22], microwave (Termatrac(tm), Ormeau, Australia), and so on. For instance, a termite monitoring system using an acoustic emission (AE) sensor has been applied to detect the noise signal of termites feeding on wood materials. Based on acoustic signals generated by termites when attacking wood, using a discriminant analysis, the acoustic feature in the termite detection system could reach an accuracy of 83.75% [13]. But it should be noted that the noise made by termites can be very easily interfered with by ambient sound signals [14]. The accuracy of this AE sensor-based termite monitors is increasing with the help of the developed algorithm and analysis strategies. The support vector machine (SVM) with polynomial kernel function achieves the best classification accuracy of 0.9188 [14]. Based on a termite bait station, [PERSON] (2001) described a sensor consisting of a wooden stake which was painted with a conductive circuit of silver particle emulsion [17]. The sensors were wired to a data logger and a host computer and formed a computerized remote monitoring system. The mean monthly accuracy at 6 months after installation ranged from 41 to 79% [17]. Additionally, when the dimensionally stable sensor was used instead of a wood sensor, the accuracy was significantly improved compared with wooden sensors.