Yellow Jackets Use Alarm Pheromones To Mark Intruders and Rally Colony To Attack

When you disrupt a yellow jacket's hive, you don't just suffer the wrath of a single angry wasp, you suffer a swarm attack. That's because yellow jackets are highly protective of their helpless young and adults emit chemical signals known as alarm pheromones that basically rally the colony into action and mark intruders for attack.

In order to study this complex defensive behavior, a team of researchers led by Dr. Sean McCann of Simon Fraser University created a unique, but simple, device that allowed them to locate the species-specific alarm pheromones in three wasps: the western yellow jacket, the common yellow jacket and the German yellow jacket, according to a news release.

"We developed a new and standardized method to evaluate alarm pheromone activity in yellow jackets and other social wasps that is inexpensive and easy to use. The device we constructed uses off-the-shelf components, and consists of a pair of black targets enclosing a pair of microphones," the authors wrote in their study. "A test substance and a control can be applied to each target, and then a stereo audio file is recorded at the nest site. When wasps hit the black targets, it makes a percussive sound, almost like a drum. The resulting stereo file is then split and analyzed with an open-source software program to count the number of strikes received by the treatment and control targets." (Scroll to read more...)

Social insects, such as yellow jackets, invest a lot of time and resources in their colonies, so they tend to be protective of what they have worked hard to build. During early stages of life, protein-rich larvae inside the hive remain defenseless, so many of the adult wasps work together to raise them. Part of ensuring the young develop into strong adults is keeping large predators away from the nest.

Using their black targets, researchers were able to automatically count the number of wasp strikes, which were then used to determine which species have alarm pheromones and whether each individual species could recognize the alarms of another. Certain wasp strikes were recognized by amplitude peak, duration and interval. 

"We found evidence for alarm pheromones in all three species, and that each species recognizes and responds to the other species' alarm pheromones in similar ways," researchers added. "We conclude that the chemical messages produced by these three yellow jacket species must be very similar."

Being able to recognize the alarm pheromones of another species is advantageous for those nearby, so that they can get a jump start on stinging away to predator before it comes to close to their own colony. A wasp's alarm pheromones are contained in it venom sac, which researchers confirmed through a series of dissections. 

Their findings were recently published in the Journal of Hymenoptera Research.

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