Honey bees use animal droppings to repel ‘deadly’ giant hornets

Bees spread animal droppings at the entrance to their hives to effectively ward off giant hornets.

What’s the best way to keep giant hornets away if you are a honey bee? Animal dung, according to a very first study from the University of Guelph.

University of G researchers found honey bees in Vietnam collect and apply animal dung stains around beehive entrances to deter fatal nest raids by an Asian hornetVespa soror) whose North American cousins ​​have been nicknamed “murderous hornets”.

This discovery is also the first to document the use of tools by bees.

An invasive North American species native to Asia, giant hornets are almost as long as a golf tee and contain about seven times as much venom in a single bite as a regular bee.

Deadly hornets (V. mandarinia) were discovered in 2019 in British Columbia and Washington. The arrival of the poisonous insect in North America has raised concerns about human security as well as threats to bees and local ecosystems.

Professor Gard Otis of the University of G

“Giant hornets are the biggest wasps that threaten bees. They are one of their most important predators, ”said the environmental science professor.

Otis conducted the study with lead author Heather Mattila, who completed her doctorate at the University of Guelph in 2006 and is now a professor of biology at Wellesley College in Massachusetts. The other co-authors were former University of G graduate students Hanh Pham and Olivia Knight, as well as Ngoc Pham and Lien Nguyen in Vietnam.

Recently published in the journal PLOS ONE, the study was conducted in Vietnam, where researchers from the U of G studied V. soror.

These two species are the only hornets to recruit nest mates in organized attacks that can lead to breaches in the nest, Otis said. Hornets attack nests, killing bees and carrying larvae and pupae to feed their own developing brood.

The researchers found that the bees had developed a preventive defense by collecting animal droppings and applying them to the entrances of the hives.

“This study demonstrates a pretty remarkable trait that these bees have to defend themselves against a very bad predator,” Mattila said.

She said that unlike their Asian counterparts, honey bees in Canada do not have similar tusks. This means that North American beekeepers should rely on the destruction of hornets’ nests, or hope that the weather or other factors will limit the spread of hornets.

Referring to Apis mellifera, the species of honey bee commonly found in Canada, Mattila said, “They haven’t had the opportunity to evolve the defenses. It’s like going into a cold war.

Otis started the project after asking beekeepers in Vietnam about brown spots at the entrances of Asian bee hives. As part of a successful beekeeping development project funded by the Canadian government, he facilitated fall workshops from 2007 to 2011 in rural villages with high levels of poverty.

During a visit, an experienced beekeeper explained that the substance was buffalo dung. Every beekeeper Otis has worked with have linked these hives with hornets. “Collecting droppings is a behavior never before reported for bees, and no one had studied the phenomenon,” he said.

In 2013, the U of G team received US $ 25,000 from the National Geographic Society for the study.

Researchers collected droppings from water buffaloes, chickens, pigs and cows and placed them in mounds near an apiary. By the end of the day, some 150 bees had visited the heaps, especially collecting more fragrant manure from pigs and chickens.

The team tagged individual bees to identify them in their hives. Minutes later, they recorded videos of the tagged bees applying the material to the entrances to the nest.

Hornets spent less than half the time at entrances to nests with moderate to heavy manure spots than in hives with few spots, and they spent only a tenth of the time chewing at the entrances to the hive to reach the brood of bees. They were also less likely to launch massive attacks on the more spotted hives.

Researchers aren’t sure exactly what deters hornets, although they suspect the insects are repelled by the scent of dung. Feces can also mask odors emitted by bees.

To better understand hornet behaviors, the researchers extracted the chemical pheromone applied by the hornets when tagging their target hive. When the pheromone was applied at the entrance of the bees, it prompted the bees to apply dung to the hive.

Many scientists disagree that some animals – not to mention insects – use tools.

To qualify as tool users, animals must meet several criteria, including the use of an environmental object – in this case, dung. The bees are clearly using the material to modify the hive for a specific purpose, Otis said. And they shape and mold it with their mouthparts, which he says meets the test of holding or handling a tool.

Beekeepers in Vietnam normally control hornets by standing guard and crushing individuals, preventing them from escalating their attacks.

“If you allow them, a group of hornets gather together, attack the colony and take over. Beekeepers check them daily by moving among their hives and hitting hornets.

Otis said he was initially terrified of working near the giant hornets. The hazardous material protective suits typically worn by Japanese researchers were impractical in the Vietnamese heat, he added. Within days, the team learned that hornets weren’t on the defensive when they were in the apiary and away from their own nest.

“I got stung by one and it was the most excruciating sting of my life.

Reference: December 9, 2020, PLOS ONE.
DOI: 10.1371 / journal.pone.0242668