Radio frequency identification (RFID) tags are now available at a scale—weighing about 4 milligrams each—that makes them useful for attaching to insects such as honey bees. (Photo credit: Sebastian Shepherd, Ph.D.)

Sebastian Shepherd, Ph.D.

By Sebastian Shepherd, Ph.D.

Radio frequency identification tracking, commonly known as RFID, is revolutionizing what is possible in entomology, but what is it about this technology used in retail inventory, package tracking, and contactless credit cards that is useful for studying insects?

For thousands of years, humans have tried to track insects. Honey gatherers tried to track bees to locate the golden sweet rewards of a bee hive. Antiquated methods of detecting the movements of bees sound just like the ancestral wildlife tracking used by big-game and large-mammal experts. Bees were tracked by looking for droppings on leaves. Bees were also tagged with natural products to make them easier to see—such as ochre, blades of grass, and even the hairs of an ox—and then “pursued” by honey hunters. Not a particularly easy occupation!

Long before the advent of electronic tracking devices, some honey hunters relied on animals such as the greater honeyguide bird (Indicator indicator) to lead them to bee hives. (Photo credit: Flickr/Gisela Gerson Lohman-Braun, CC BY-SA 2.0)

These methods were so difficult that some honey hunters relied on other animals such as the greater honeyguide bird, Indicator indicator (right), to lead them to bee hives.

It took centuries for other innovations such as numbered paper tags that could be stuck to bees. Even these, in most cases, just help identify a queen bee, but sometimes entomologists might use number tags to tell individual forager bees apart. This might require many painstaking days in a bee suit counting and timing the flights of different individual bees among all the buzz and commotion of a hot summer afternoon. In other areas of entomology, insects could be painted with colorful powders or glowing ultraviolet dyes. All in all, though, these methods require patience, a very keen eye, and a lot of time and energy.

Fast-forward to 21st-century science, and if you look at the range of behavioral tracking technologies in wildlife ecology, we’ve really moved on. Radio telemetry allows you to track the specific movements of individuals over large landscapes, and innovations such as the global positioning system (GPS) means that remote animal tracking is at the scale of medium-Earth-orbit satellites.

But there’s a problem when you try to apply this technology to insects. Unfortunately, a lot of these modern-day innovations require a battery-powered transmitter to track the animal you want to record. Easy enough when you want to monitor a 12,000-pound minke whale, but what kind of transmitter can a 0.00025-pound bee carry?

Luckily, some ingenious entomologists have been working on these problems, and our abilities to track insects in the field are getting better by the day. For example, in radio telemetry batteries now exist that are small enough to track the complete pattern of movement of an individual insect. However, these trackers are still too big to fit on all but the largest of insects. For example, the movement ecology of large insects like beetles and crickets has been studied with radio telemetry.

Tracking technology has advanced to the point that some devices are small enough to be attached to bumble bees (such as this Bombus terrestris), though battery-powered devices remain too big for all but the largest of insects. The transponder on this bee is unpowered and weighs about 15 milligrams (while battery-powered units weigh about 200 mg) and can be tracked using harmonic radar. (Photo credit: Wikimedia Commons/Andrew Martin, CC BY 2.5)

Another method of insect tracking is harmonic radar. Requiring no batteries, this overcomes the weight problems; however, with no power source to produce a unique signal, the main drawback of this method is that it is difficult to distinguish individuals that are tagged at the same time, and this method can be susceptible to signal interference. When implemented well, harmonic radar has been used to study the complete flight paths of a range of insects, including bumble bees and moths (to name a couple).

In my own entomological research on honey bees (Apis mellifera) I want to distinguish many individuals at once, and I want the tags to be lightweight. This is where RFID can fit in for me and for many other entomologists.

RFID is kind of like a license plate for insects. RFID does not allow me to track the full movement trace of an individual over time, but rather it will record whenever an individual passes by the location of an RFID reader. Using the same kind of technology that is used in credit cards and the packaging industry, I attach tags with unique identifiers to the bee that I’m trying to track. I then place RFID readers in locations where I might expect the bee to go, such as the entrance to a hive or a sugar feeder. Every time a bee with a tag arrives in proximity to the reader, it records the tag, with a timestamp, so I know when that individual came by. As a result, whereas with harmonic radar and radio telemetry I’d get data like GPS navigation, a descript track of exactly where that individual travelled in space, RFID is like a highway toll-pass or license-plate reader. It knows which individual is which, where and when each one arrived, and thus how long it took that individual to go between each gate but not exactly what the individual did between the gates.

Radio frequency identification (RFID) tags do not emit a signal on their own but rather can be read by powered RFID readers if and when those tags pass within range of the reader—a setup essentially the same as highway toll-pass or license-plate readers. (Photo credit: Wikimedia Commons/Mrschimpf, CC BY-SA 3.0)

This makes RFID perfect for tracking bees (and other insects which live in colonies), because I know the location they will come and go from (the hive). I can tell what time a bee left and returned to a colony, the frequency of trips made per day, and even time spent at certain locations.

A honey bee (Apis mellifera) with radio frequency identification (RFID) tag approaches a hive. An RFID reader placed at the hive entrance senses the tag and records the unique ID of the bee and the exact time it entered. (Photo credit: Sebastian Shepherd, Ph.D.)

This kind of technology has been implemented to understand the impacts of pesticides on bee foraging, mating biology of honey bee queens, and how fungal infections affect honey bee flight behavior, just to name a few studies. In my own research, I use RFID technology to investigate how the foraging behavior of honey bees is affected by a variety of environmental stressors.

But honey bees aren’t the limit of RFID technology. This technology works well in tracking other insects in colonies such as bumble bees and ants, and it has even been suggested for use in insects such as mole crickets and billbugs. One of the key challenges of RFID technology is “predicting” where the individual you’re tracking will be so that you can set up the RFID readers to detect your study insect. But, if you can do this, you have a setup that lets you remotely track the locations and movement of hundreds of individuals, for as long as you power the setup and as long as the tag stays on. So, in a modern entomologist’s toolbox, RFID is an incredible technology, which is now commercially available and can provide versatile data for the right study questions.

Sebastian Shepherd, Ph.D., is a postdoctoral research associate in the Department of Entomology at Purdue University. Twitter: @sebshepherd. Email: shephe24@purdue.edu.