Using electrostatic fields to 'spy' on honeybees can inform us about their health — and the environment's

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An Africanized honeybee (left) and a European honeybee on a honeycomb. (USDA Agricultural Research Service/Scott Bauer)

Researchers have developed a technique for "listening" in on the electrostatic signals honeybees emit to communicate with one another, allowing scientists to gather information about the health and behavior of the bees directly from the source.

The study, published April 28 in Frontiers in Behavioral Neuroscience, is the first to use this technique on bees. Senior author Randolf Menzel, a professor emeritus of neurobiology at Freie Universität Berlin, spoke with The Academic Times about the project, explaining that bees are generally studied from the outside in, either through visual observation or through microphones.

Listening to electrostatic signals produced by the bees themselves for communication is akin to spying on them, because electrostatic data can be gathered unobtrusively during regular beekeeping, unlike most visual observation methods.

"By picking up the signals of the bees that they produce themselves, not any physical kind of parameters, this is directly listening to the bees inside of the colony," Menzel said. "And, indeed, when they become unhealthy, if they are treated with pesticides or if they have a biological situation, like preparing for swarm or [losing] their queen, then the way they talk to each other is very different, and we can pick this up and we measure it."

Despite humans' reliance on bees to pollinate one-third of crops, colonies have been declining at an alarming rate for several decades: The number of hives in the United States has fallen from 6 million in the 1940s to 2.5 million today, a decline of 140%. Cracking the mysteries of bee behaviors should provide insights that can help in their conservation. 

More broadly, bees and their hives are highly sensitive to environmental stressors, including pesticides and climate change, and, as the study puts it, can act as a "canary in the coal mine" for the health of the wider environment, identifying sources of harm earlier than is possible when studying larger organisms.

As the study reports, "Honeybees are the most important pollinators of fruit-bearing flowers, and share similar ecological niches with many other pollinators; therefore, the health of a honeybee colony can reflect the conditions of a whole ecosystem."

The electrical signals that bees generate are mechanical in nature. Due to friction, honeybees pick up an electric charge when they fly, like how humans can pick up a small static charge when walking across certain carpets. The honeybees then transmit this electrostatic energy through movement, sending tiny signals to other individuals in the hive. 

The challenge for the researchers was developing a system that could capture these tiny signals, because they are undetectable from all but the closest ranges.

"It's not a global system," Menzel said. "It's a localized signal, and they use it for inter-individual communication."

The researchers worked with 30 beekeepers across Germany for five years to gather their data. They used a special hive designed to act as a Faraday cage, an enclosure made of a continuous covering of a conductive material that can block electromagnetic fields. This ensured that whatever signals were captured within the hive were generated by the bees.

The team used a series of sensors to monitor the electrostatic output of the bees during their regular behaviors in the hive. The researchers were especially focused on the waggle dance, in which honeybees walk in unique patterns while wiggling their abdomen to indicate the location of a food source. 

"Other bees follow the dancing bee, read the message of the dancer, and apply the information about distance and direction to an attractive food source in their outbound flights," Menzel said.

The team saw that different behaviors triggered different patterns in electrostatic fields from the bees. And while some of these differences occurred during normal bee behaviors, such as preparing to swarm, the researchers also discovered new behaviors from bees, such as performing waggle dances at night. The study also found that insecticides, which were applied to some hives to treat against invading pest mites, had a negative impact on the bees' communication.

While the signals that bees produce can provide useful information, Menzel warns that scaling the technology to use on wide areas would be challenging because the signals involved are so minute. 

"To get meaningful knowledge about the impact of pesticides and health conditions of bees in a larger area, we will have to use many devices across that area," he said.

However, the upside to this micro-scale signaling is that the bee signals operate at wildly different frequencies and voltages than human-generated electricity. So the researchers suggest it is unlikely that technology such as cell phones and power lines can interfere with the bees.

Though this aspect of bee signaling was not tested explicitly by the researchers in this study, Menzel illustrated his hypothesis with an example: "You take a normal power cable and put it in the colony, the insulation is in the range of two millimeters, or maybe three millimeters," Menzel said, referring to the thickness of rubber insulation around electrical cables. "[This] is already reducing the field strength so much that the bees [only] just sense it, and they are not disturbed."

While the present study was primarily intended to confirm that the new recording system is feasible, Menzel maintains that there is much work to be done on how to interpret the results of the monitoring system.

"So far we have only begun to apply machine-learning algorithms to separate and quantify the electrostatic field signals," he said. "We have experience over the last five years on this new applied system. And we have collaborated with more than 30 beekeepers who have used it over the years, but it's also clear that we can improve on speed and accuracy and on numbers."

The study, "The electronic bee spy: eavesdropping on honeybee communication via electrostatic field recordings," published April 28 in Frontiers in Behavioral Neuroscience, was authored by Benjamin H. Paffhausen, Julian Petrasch, Uwe Greggers, Aron Duer, Simon Menzel, Karén Haink, Jana Čavojská, Sophia Wutke, Anja Voigt, Josephine Coburn and Randolf Menzel, Freie Universität Berlin; Zhengwei Wang and Peter Stieber, CAS Key Laboratory of Tropical Forest Ecology; Morgan Geldenhuys, independent researcher; and Timo A. Stein, Technische Universität Berlin.

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