## 3 Technological Advancements in Bee-Based Biosensors/Biomonitors
### Detecting and Tracking Bees Marked with Tags  
Major developments in the fields of electronics and bees were initiated in the mid- to late 1980s by a research team at Oak Ridge National Laboratory (ORNL). [PERSON], an ORNL engineer and beekeeper, lead an effort to identify and track Africanized bees. First, an acoustic detector to discriminate between European and Africanized bees was developed and patented [45]. This was a hand-held instrument with a clear capsule into which a bee could be released and allowed to fly toward the light of the sun. Frequency filters analyzed wing-beat frequency, and a warning light indicated detection of Africanization. This device discriminated European honey bees from the Africanized variant based on subtle differences in the wing-beat frequency of these two strains of bee. Second, his team produced an electronic tracking chip for bees [43] that was glued onto the thorax of the bee. The chip weighed less than 35 mg and was about the size of a half-carat diamond. It achieved its low weight by eliminating batteries, instead using tiny solar collectors for power because batteries would have been too heavy. The transmitter chip had a range of about a mile and used a ground-based sensor to  
Figure 3: Wood’s Apidictor for honey bee colony swarm detection. read infrared light pulses from the chip. None of these devices became commercially available. Catching bees to put in the acoustic detector was problematic, reliable discrimination across the full-range of hybridization between the two different strains of bees was difficult, and the tracking chips and readers were too expensive for general use. The next major development in tracking bees was by [PERSON], [PERSON] and [PERSON] of the United States Department of Agriculture's (USDA) Carl Hayden Bee Research Laboratory in Tucson, Arizona. They studied queen mating using x-band radar to document drone flyways and congregation areas [50,51]. Because drones are larger than worker bees and congregate in large numbers in mating areas, no markers were needed to identify drones in their studies. Radar is best suited to large masses of insects, e.g., swarms of insects, but can detect small insects at close ranges and large insects at longer distances. Without reflective tagging, however, radar cannot track individual insects. Shortly thereafter, [PERSON], at the Natural Resources Institute (NRI) Radar Unit, Worcestershire, UK, and his team of engineers and investigators re-visited the chip marker approach to tracking bees. An idea to track bees came from the Rothamsted Experimental Station; NRI solved the problem [52]. The NRI unit later became part of Rothamsted Research. [PERSON]'s team successfully followed flying bees using hand-held readers and harmonic radar chips fastened to bees (Figure 4) [53, 54, 55, 56, 57]. Unlike most other radio-frequency tags, harmonic radar tags re-radiate the radio-frequency (RF) signal at twice the frequency; a 917 MHz signal will be returned at 1845 MHz. Figure 4: Harmonic radar marking and tracking chip. Note the tall, vertical antennae. Although harmonic radar was developed at NRI, the idea to track bees came from Rothamsted Experimental Station. The NRI Radar Unit later became part of Rothamsted Research, and remains there. Drawbacks of harmonic radar were and continue to be: (1) the large size of chip-borne antenna required to increase the detection distance for tracking; (2) the difficulty of tracking insects in a cluttered environment; and (3) the inability to identify individuals in a tagged group of insects. The antenna can and often does alter normal flight, although it is less of an issue with bubble bees which are often considerably larger than honey bees. Still, there have been several honey bee-tracking studies published using this technology, and at least two published reviews [52, 57]. Some of the studies, discussed at the end of this article, address the dance language.