## 3 Technological Advancements in Bee-Based Biosensors/Biomonitors
### Detecting and Tracking Bees Marked with Tags
The latest is a 2014 study using harmonic radar to detect the effects of _Nosema_ infection on the homing ability of honey bees [58]. Where antenna length is not an issue, harmonic radar is a very useful technology. Harmonic radar systems are commercially available and are routinely used for finding avalanche victims. One of our students used it for tracking salamanders, and large insects like butterflies and some beetles can easily carry a harmonic radar tracking tag. DARPA funded the next iteration of even smaller RF chips in late 1999. We also tested miniature radio frequency (RF) pit tags and hive-mounted readers developed for us by a group of engineers directed by [PERSON] at Pacific Northwest Laboratory. Each 27 mg RF tag was about half the size of a rice grain and contained a 10-character code which identified an individual bee. When the bee entered or exited the hive, an electronic tag reader recorded the passage. Unfortunately, we concluded that our miniature chip was still large enough to alter normal bee flight and that read range was limited to centimeters [59]. Much progress in RF tags has been made in the past decade. Tiny passive tags using nanoblock technology are now employed for inventory control in warehouses and stores such as Wal-Mart. In fact the tags produced by Alien Technology, a world leader in volume production of Radio-Frequency Identification (RFID) products, were produced by [PERSON]'s team--the same team that placed the first RFID tag on a bee for us. Small and light, passive (2-3 mg) RF bee tags became commercially available around 2006 in Europe. These have been used to study a variety of bee and colony behaviors, queen mating flights, and the effects of neonicotinoid pesticides [60, 61, 62, 63, 64, 65, 66, 67]. A particularly ambitious study was launched in 2014 in Tasmania, Australia, where 5000 bees were tagged to study bee movements as the tagged bees passed stationary readers [68]. Other investigators [69] mounted even smaller RFID (Figure 5) tags on the thoraxes of bees to study inter-individual variation within a bee colony and plasticity in honey bee foraging activity. Typically, small RFID tags usually have read distances of less than 50 cm; the smallest bee tags have a range of \(\leq\)20 mm. To this day, the read range of small passive chips mounted on insects tends to be very limited (in the millimeter to, at most, centimeter range), greatly reducing the detection probability of any marked bee in a free-flying environment. Whether using harmonic radar or RFID tags, the engineering limitation is that detection distance is a function of frequency and antenna size. Antennas (Figure 4) on tracking chips increase range of detection but add weight and interfere with bee flight behavior. The newest bee tags use an antenna printed on the chip and in one novel study, we experimented with the laser-plating of fractal antennas onto the bees themselves, working with a USNaval Research Laboratory. Active, or powered, chips have greater range than passive tags, but batteries add weight. The solution may be using the insect itself to power the tag. DARPA continued to focus on developing RFID tracking chips. This resulted in a smaller chip, produced by Mayo Research Institute, followed by efforts to extend the range to one kilometer, which were attempted by at least one large military contractor. To our knowledge, none of these chips have progressed beyond prototypes, despite large financial investments made in developing RFID for long-range location and tracking of insect biosensors. What is clear is that interest in hive- and bee-based sensors, often with advanced, miniaturized electronics has become common enough that there is sufficient information to warrant a book about this and related subjects [60].