Bees can sense the electric field of a flower, unless the fertilizer spoils the buzz

Bees can sense the electric field of a flower, unless the fertilizer spoils the buzz

Bees are familiar with the unspoken language of flowers. These noisy pollinators are consistent with many of the traits of flowering plants—the shape of the bulbs, color variety, and their attractive scent—that bees rely on to see if a reward for nectar and pollen is nearby. But bees can also detect signals that go beyond vision and smell. The fine hairs covering their bodies, for example, are very sensitive to the electric fields that help bees recognize flowers. These electric fields can affect how bees forage—or, if these fields are artificially altered, even disrupt this behaviour.

Today in the magazine PNAS NexusAnd the Biologists have found that a synthetic sprayer fertilizer can temporarily alter flowers’ electrical signals, a shift that causes bees to land less frequently on plants. The team also tested a type of neonicotinoid pesticide — known to be toxic and harmful to honeybee health — called imidacloprid, and detected changes in the electric field around the flowers. Interestingly, the chemicals did not appear to affect vision and smell, suggesting that this lesser known signal plays a greater role in communication.

“Everything has an electric field,” says Ellard Hunting, lead study author and a sensory biophysicist at the University of Bristol. “If you’re really young, the little weak electric fields get really deep, especially if you have a lot of hair, like bees and insects.”

[Related: A swarm of honeybees can have the same electrical charge as a storm cloud]

Biologists are just beginning to understand how important electrical signals are in the world of floral signals. To distinguish flowers that are more resource-rich within a species, bees, for example, can recognize specific visual patterns on petals, such as spots on the surface, and remember them for future visits. Bloom shape is also important—larger, more open flowers may be an easier landing pad for less slender beetles, while narrow tubular bulbs are hot spots for butterflies with long mouthparts that can reach for nectar. Changes in humidity around the flower have also been found to affect hawksbill moths, as newly opened flowers usually have higher humidity levels.

The electrical signal, though, is “a very recent thing that we’ve discovered,” says Carla Eisenberg, a biologist who studies pollination ecology at Bates College in Maine, who was not involved in the study. A 2016 study found that searching for bees changes the electric field of a flower for about one to two minutes. The study authors suggested that even this brief change might be detectable by other transient bees, informing them that the flower has been visited recently — and has fewer nectar and pollen to offer.

The natural electric field of a flower is generated in large part by its bioelectrical potential – the flow of charge that it produces or occurs within living things. Hunting shows that electric fields are a dynamic phenomenon. “The flowers usually have a negative potential and the bees have a positive potential,” Hunting says. “Once the bees get close, they can sense the field.” Wind, landing of a bee, or other interactions will cause instantaneous changes to the PV potential of Venus and the field around it. Knowing this, Hunting had the idea to investigate any changes in the electric field caused by the chemical applications, and whether they prevented bee visits.

He first started with pesticides because of the well-studied effects they can have on insects. “But then I realized that fertilizers also have a charge, and they are used as well and are much more relevant on a large scale,” he says. These chemical mixtures used in agriculture and gardens often contain different levels of nitrogen, phosphorous, and potassium. Everyone is using [fertilizers]It is claimed to be non-toxic.

First, to assess bumblebee foraging behavior, Hunting and colleagues conducted an experiment at a rural field site on the University of Bristol campus using two potted lavender plants. They sprayed a commercially available fertilizer mixture on one potted plant while spraying the other with demineralized water. Next, the team watched bumblebees skip the lavender-covered fertilizer. Sprays containing pesticide or fertilizer altered a flower’s bioelectrical capacity for up to 25 minutes—much longer than shifts caused by wind or landing bees.

[Related: Arachnids may sense electrical fields to gain a true spidey sense]

But to make sure the bees were avoiding the manure due to a change in the electric field — and not due to chemical compounds or other factors — the researchers needed to re-create the electrical shift in the flower, without actually spraying. In his backyard the size of a football field, a natural area devoid of other sources of electricity, hunting manipulated the bioelectrical potential of lavender plants in order to mimic change. He put the stems in water, wired them with electrodes, and broadcast a current using a DC power bank. This created an electric field around the plant in the same way as compost.

He noticed that while the bees approached the electrically manipulated flowers, they did not land on them. They also approached the flowers to a much lower degree than the control flowers, Hunting says. “This shows that electricity alone does indeed elicit avoidance behaviour.”

Fishing suggests that the plant’s defense mechanism may be the origin of the electrical change. “What actually happens is if you apply chemicals to plant cells, it triggers a chemical stress response in the plant, similar to the wound response,” he explains. The plant sends metabolites – which have an ionic charge – to start fixing the tissues. This flow of ions generates an electric current that bees detect.

The researchers also noted that the chemicals did not seem to affect vision or smell, and interestingly enough, plants that had been sprayed with pesticides and fertilizers seemed to experience an electric field shift again after the rains. This may indicate that the effect persists after only one spray. The researchers note that the new findings may have implications for informal gardeners and major agricultural industries.

Ideally, you can use fertilizer in the soil [instead of spraying directly on the plant]Fishing says. But that would require more labor than the method many use in American agriculture, where planes spray huge fields.

[Related: Build a garden that’ll have pollinators buzzin’]

Fortunately, Eisenberg says, changes in the electric field are relatively short-lived, making it easier for farmers to find alternative solutions. For example, they can spray agrochemicals during midday, when pollinators feed less frequently because many flowers open in the morning and usually run out of pollen by then.

Isenberg says the toxicity of chemical sprays may have a greater “population level” effect on bee decline. But this study offers a new idea: that the change in voltage may need to be taken into account in order to spray plants effectively. “It raises questions about other kinds of things that might affect this potential,” she adds, “such as pollutants in the air or pollution that falls with rain.”

It would be useful to look at the effects of electric field changes in more realistic research settings over longer periods of time, Isenberg says. Fishing agrees. “Whether this phenomenon is really relevant in the long term, it may be, but we need to find out more about this new mechanism.”

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