Building Pheromone Traps to Catch Asian Giant Hornets
It was at the height of the pandemic when we were hit with a major twist. Asian giant hornets, commonly known as murder hornets, had made their way to the United States. It’s an intrigue that didn’t really pay off, fortunately. Giant hornets, known by their scientific name Tangerine Vespahaven’t really gained a foothold, at least not yet, but studies suggest they could be spreading across western North America, and they’re already posing a huge challenge in other parts of the world.
Asian giant hornets present a few unique challenges, primarily due to their large size. Their stingers are so long they can squeeze through the protective clothing beekeepers wear, they deliver a higher dose than you would get from more common bees and wasps, and the sting is painful. The good news, at least for humans, is that they are generally not very aggressive towards people. They could, however, present additional pressure for bees who are already challenged by pesticides and climate change.
With that in mind, scientists are looking for new ways to control invasive giant hornet populations and have come up with something that seems to work incredibly well. Scientists are using the hornets’ sexual urges against them. James C. Nieh of the Division of Biological Sciences at the University of California, San Diego and his colleagues identified the chemical components of sex pheromones released by virgin queens and used them to construct traps. The results were published in the journal Current biology.
“We rubbed strips of paper over different parts of their bodies and found two specific regions, the fifth and sixth intersegmental sternal glands, that are functioning. When you put the tapes in a cage with males, they go crazy,” Nieh told SYFY WIRE.
Males of the species approach strips of paper covered in natural pheromones with great interest, but things get interesting when there is more than one male in the cage. If a male had already approached the chemical-covered paper strip, another male might mistake it for a mating queen and attempt to mate with it. The combination of chemical constituents and recognizable morphology seems to be the secret code for trapping males.
Harvesting natural pheromones from queen bees isn’t really scalable, so scientists had to identify which chemical was doing the job. They used solvents to remove chemical pheromones from paper strips and used gas chromatography and mass spectrometry to identify them. In short, they pass the chemicals through a machine which ionizes them and bounces them against a list of chemicals already identified. From there, they grab those chemicals off the shelf and run them through the machine to confirm that the same pattern is present. Just like that, the team had identified the main components of Hornet Loot Calls.
They applied the chemical cocktail to sticky traps similar to those used to catch rodents and placed them about 15 meters from the entrance to a hornet’s nest. The males were attracted to the traps but did not land until the scientists added a visual component.
“We had to use a dummy male in the traps. Initially the males showed interest but none of them landed, placing a dummy male helped them do that. We think the dummy looks a lot like the female of the species. So now the trap looks and smells like her,” Nieh said.
The traps were placed relatively close to the entrance to the nest because mating usually takes place close to the nest. Tests have successfully trapped thousands of male giant hornets with this setup. One limitation, of course, is that you must already know the location of the nest. It is possible, however, that the traps work over greater distances.
“It is in the interest of the species, as of all species, to avoid inbreeding. If they were to only emerge and mate with their brethren, that would be pretty bad for the species. So we think males can be attracted from long distances,” Nieh said.
Future experiments planned for this fall are planned to try traps at greater distances. They are also looking for additional chemical components that have not yet been identified.
“Natural pheromones are even more effective, so we’re missing a compound and hoping to find out what it is,” Nieh said.
It is also possible that the males emit sex pheromones to attract the queen. If these could be identified, similar traps could be made which would be much more effective in controlling the population. In the meantime, the chemicals identified in the paper are readily available off-the-shelf and could be deployed to limit the population of breeding males.
If ever giant hornets decide to pick up the wire and come looking for us with our guard down, we’re ready for them.