Luring Murder Hornets Using Sex Pheromones May Eliminate Them Effectively

We all remember the viral picture or news about Asian giant hornet coming to the United States back in 2019. If we recall correctly, the sudden invasion sent researchers and everyone else to eliminate them.

It wasn’t without good reason, of course. The East Asia and Japan native species, called Vespa mandarinia, can destroy native beehives and honeybees in a matter of hours.

When they’ve managed to infiltrate a nest, they remove the hive’s brood and take bee larvae and pupae back to their nests to feed their own young,

In short, these baddies threaten bee-pollinated crops worth over $3 billion annually in Washington state only.

Well the good news is, scientists have found a solution: using the insect’s sex pheromones against hornets that are eager to mate.

Femme fatale

It all began when researchers placed synthetic pheromones in field traps that mimicked hornet queens produced. Once they did that, hundreds of males flocked to the site.

Study author James Nieh said, “We were able to isolate the major components of the female sex pheromone, an odor blend that is highly attractive to males who compete to mate with virgin queens.

“When these components or their blend was tested in sticky traps, they captured thousands of males.”

How did they get the pheromones? The entomologists got it by swabbing various virgin giant hornet queens captured in Yunnan, China.

Then, they swabbed each of the queen’s sex glands and used technology (namely gas chromatography and mass spectrometry) to find out the compounds that lure in male murder hornets.

The top three compounds in the queen’s pheromone were hexanoic acid, octanoic acid, and decanoic acid.


Vespa mandarinia japonica by Yasunori Koide Wikimedia Commons


For those of you who are not familiar with the acid’s odor, like me, here’s a bit of a picture: hexanoic acid has a fatty, cheesy, or urinous odor. On the other hand, decanoic acid is pungent and found in fruit flavorings, while octanoic acid is found in animal milk.

When the researchers test the compounds on the male hornets, they saw their antennas retracted; a sign of attraction in the insects. The results were the same when each compound was tested individually and then mixed.

Pheromones that trap?

Next, in order to test out the pheromone further, they made traps from a sticky board, a fake male hornet, a glass tube filled with the odorous acids, and another tube filled with extracts from the queen’s glands.

The result? Male hornets made a beeline for the queen’s natural pheromones, but they also were attracted to the synthetic mix. In total, the queen’s pheromones attracted about 500 male hornets, more than twice the number drawn by the three-chemical concoction.

So, the synthetic mix leads to a fewer result. Therefore, the team believes that there are other compounds in the queen’s pheromone that they need to identify in order to make a more effective trap for male hornets.

All is not lost, though, for the study could bring scientists closer to identifying easy ways to trap the invasive insects. So far, the efforts are not as easy because this species are elusive and create well-hidden nests.

Previously, scientists have removed hornets after identifying a nest and using a vacuum to trap them in a tube. It’s the identification of the nests that’s a little time-consuming.

“The sooner we find a reliable way to attract males and find nests, the better,” said Timothy Lawrence, a bee scientist at Washington State University who not involved with the study.

You can read more about this research in Current Biology.


Asian giant hornet by Fufill Wikimedia Commons



Asian hornet’s vs Asian honeybees

There’s one interesting thing that we should know: not all honeybees are totally defenseless to hornet attacks. Maybe you’ve seen videos online about bees swarming a hornet until the attacker dies. Well, that’s the species: Apis cerana or Asian honeybees.

Other than forming a ball to suffocate attacking hornets, the bees will warn hive mates. When they sense nearing hornets, they warn others of an impending attack with their bodies, vibrating their wings to make a noise comparable to a scream for help,

First author Heather Mattila said, “Our study showed that the bees didn’t make the sound if there weren’t any hornets. It was made very infrequently in response to smaller hornets, a bit more often if the bees smelled a giant hornet (but didn’t see one), and they made them by far the most when a giant hornet was directly outside of their nest.”

Not just screaming and swarming

In this study, the researchers focused on how Asian honeybees react when the Vespa soror, another species of giant hornet, threatens a honeybee hive.

Mattila and her team first took note of the Asian honeybee’s alarming call after hearing it while documenting the honeybee’s use of animal dung to ward off hornets in Vietnam.

Yep, the bees used good old dungs to counter-attack the hornets. This practice is called fecal spotting, and researchers found that hornets were less likely to chew into honeybee hives if the entrances were lined with poop.

The team noticed that whenever giant murder hornets were near, noise levels of the hives shot up.

Mattila explained, “We could hear the bees’ sounds from several feet away. So, we started popping microphones into colonies so that we could eavesdrop on them”

After such observations, the scientists recorded the bee’s highly organized behavior in hives of local beekeepers.

Alerting hive mates when hornets are near



In the experiment, researchers recorded the honeybee soundscapes and behaviors while hornets were near, when hornets were not present, and when paper soaked in hornet pheromones was placed near the hive

After 30 hours of bee noises analysis, the scientists found that even if the nest was not under direct attack by hornets, the hive was bustling with activity if hornets were near.

The bees would start communicating with each other by vibrating their wings and thoraxes in a frantic motion. When Asian hornets or their scent is present, the hives are louder.

Mattila said, “They make them in rapid series, and so it sounds like a siren that’s going on and on and repeating. They change a lot in tone; they’re really harsh and noisy.”

After being alerted by their hive mates, the bees gather at the hive’s entrance and begin other defense actions against the hornets. As mentioned, their defenses include dung-smearing and forming bee balls to squeeze and suffocate incoming hornets.

Thus far, Mattila and her team suspect that the noise may function as an alarm signal, as it peaked when hornets hovered outside the colony’s entrance. However, they still don’t fully know why the bees scream.

Additionally, the researchers noted that when bees create the sound with their thoraxes and wings. And when they do that, they expose a pheromone-producing gland, which may be another communication strategy to rally more bees.

Seems like pheromones play a big role in saving the bees, don’t you think?

So, in the future, the scientists are planning to research the gland’s purpose.



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