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Science

Sweetness of flowers key to calming bees

Floral fragrances calm down honeybees during attacks, according to a new study. However, that's only if these odors indicate a good meal for the bee. It appears food is just more important than defense.

If only human conflicts could be solved this easily.

Presenting appetizing floral odors to honeybees negates any aggression in these animals, Australian and French researchers have found.

One of these anti-aggressive scents is lavender, Morgane Nouvian, along with her team of colleagues at the University of Queensland in Brisbane, asserts.

"These compounds are associated with floral rewards and elicit feeding or foraging, thus preventing the bees from engaging into defense,"

they wrote in the journal Nature Communications.

Their results could help beekeepers keep their hives calm, the researchers concluded.

Studies show that between 14 and 49 percent of all beekeepers have developed an allergy against bee venom.

aggressive honeybee Photo: David Vogel (CRCA)

Front legs of the ground and antennae pointing forwards: a bee is on alert and about to attack

Why bees get aggressive

Isoamyl acetate is a very powerful chemical compound, and it is the main ingredient in the honeybee sting alarm pheromone.

When a specific subset of worker bees called guards notice something indicating a possible intruder, they emit this pheromone. Dark, moving objects are a common trigger.

Shortly after the emission, excitement unfolds in the hive, as the bees fly out to try and harass and sting the perceived intruder.

But this defense mechanism can come with the ultimate price. If a bee stings into human skin, for example, the stinger apparatus of the animal is detached and stays in the wound. The bee dies a few hours later.

Bees in the arena

In their study, the researchers triggered aggression in honeybees by rotating a black leather patch inside a glass vessel.

They introduced their bees inside this "arena," as they called the vessel, and roused them additionally with a black feather.

Sooner or later, the bees got peeved and attacked and stung the leather patch.

In some experiments, the researchers also released alarm pheromone into the chamber leading to even more attacks.

By additionally introducing odorants into the glass vessel, Nouvian and her colleagues could investigate how the bees' reaction changed in the presence of these substances.

aggressive honeybees Photo: David Vogel (CRCA)

Aggressive honeybees are stinging a leather flag. As a bee pulls away from the leather, it will lose her sting.

Not all floral scents work

Two chemical compounds decreased aggression in honeybees: 2-phenylethanol and linalool. Both are found in essential oils and emit a pleasant floral odor, with linalool showing an additional touch of spiciness. It is produced by mint herbs.

When presented with these odors, the bees were pacified and decreased their attacks against the black patch.

Lavender had the same effect. It is a mixture of linalool and one other odorant.

Other floral scents like limonene - the main odor constituent in citruses - didn't impress the bees at all; they continued attacking with the same frequency.

The researchers surmised that all honeybees have innate preferences for certain fragrances that indicate rewarding nectar-bearing plants.

Decision-making in bees

Were the flower fragrances just stronger than the odor of the alarm pheromone so that the bees couldn't detect the pheromone? The researchers exclude this possibility. Their experiments, they say, show that "these floral odors act as appetitive signals for bees."

Honeybees weigh different odorous stimuli and decide which one is the most important, the researchers concluded. And obviously - food is the most important thing on earth. At least, the research seems to show, it is more important than fighting.

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