Both a fluorescent marking system (FMS) and a portable harmonic radar system (PHRS) are effective insect tracking methods. Prior to comparing their efficacies, we tested the viability of FMS in detection of an agricultural pest, Riptortus pedestris (Hemiptera: Alydidae); previous studies showed the harmlessness of PHRS on R. pedestris and its detection distance. Fluorescent marking allowed the detection of marked R. pedestris from > 25 m, when illuminated with a laser in the dark, while affecting only the vertical walking distance of the insect. Then, we assessed the efficacy of the FMS and PHRS as well as combining both methods (BOTH) in detection of R. pedestris in a grass field and a bean field during day and night. PHRS and BOTH showed higher detection rates than FMS in all settings, except for in the bean field at night. Also, although BOTH did not enhance total detection time, it facilitated the retrieval of the sample at night compared to only using PHRS.

Various techniques have been developed to monitor insect behavior in the field. Harmonic radar tagging is a promising method of tracking target insects because it can allow efficient detection of the insects with negligible effects on their behavior or physiology. However, availability of the light limits the effectiveness of the method as it is almost impossible to spot an insect in the dark. On the other hand, fluorescent-marking, when combined with strong light source, makes the organisms distinct at night in a non-destructive manner. Therefore, we conducted a field experiment to determine the effectiveness of the combination of the two methods. Riptortus pedestris (Fabricius) adults were marked with both harmonic radars and fluorescent paint. The marked insects were haphazardly arranged and pinned onto trees or the ground in the forest at night. Then, a group of paired researchers, one equipped with a harmonic radar and the other with a hand-held laser, attempted to find R. pedestris within 20 minutes. The detection rate showed a high variance ranging from 40% to 100%. Thus, with a proper training, harmonic radar system combined with fluorescent-marking can be a powerful technique to detect insects in the field. With these equipments, tracking insect behavior in the field will be more efficient in the dark.

The use of radar systems for entomological research offers new opportunities that allow continuous tracking of individual insects in natural settings. In particular, harmonic radar systems can be applied for small animals such as insects because the radar tag does not rely on battery power, allowing them to be light weight. To apply this technology, it is essential to develop procedures to securely attach radar tags on target insects and thereafter demonstrate no adverse effects of radar tag attachment on insect survivorship and behaviors. In this study, we developed procedures to securely attach harmonic radar tags on adult Riptortus pedestris (Fabricius) (Hemiptera: Alydidae) and verified there were no detectable adverse effects of radar tagging on R. pedestris survivorship and walking or flight capacity. With the radar technique, future studies will focus on understanding dispersal capacity and pattern of R. pedestris in diverse landscapes. This will help enhance monitoring and management programs for this pest.

Pine wilt disease (PWD) is one of the most serious forest tree diseases and now the damaged area covers 7,877 ha and more than 60 cities in Korea. The causal agent of PWD, Bursaphelenchus xylophilus is transmitted by the insect vectors, pine sawyers (Monochamus spp.). Spread of PWD damage and control effect for PWD are directly related to dispersal potential of Monochamus spp. vectors. Recently, harmonic radar technology has been applied as a means for tracking individual dispersal of tagged insects. Tracking insects with harmonic radar system is similar to a mark-and-recapture technique, in which an organism is tagged, released, and recaptured. Our objective is to develop a harmonic radar tracking system by using lightweight tags to investigate dispersal of Monochamus spp., insect vectors. The harmonic radar system consists of two parts: a commercially available, light-weight (1.6 kg), handheld transceiver (RECCO Rescue System) and a small tag that reflects the transceiver signal (917 ㎒) at harmonic frequencies (1,834 ㎒). A tag consists of a miniature diode (Toshiba ISS350) with wires (36-gauge tinned copper) soldered using conductive epoxy on each side to produce a dipole antenna. These tags were evaluated in an open field to assess their maximum detection range, and at tag length of 13 ㎝, the tag was detected at >100 m.