Invisible Chemical Languages and Their Role in Insect Management

Humans are not the only animals that talk to each other. Did you know that insects communicate by sending invisible chemical messages through the air? These conversations span subjects like where to have dinner, where the safe spaces are to hide, and details for romantic dates. Scientists can eavesdrop on these conversations and distort the messages—sometimes to our benefit. Read on to see how researchers direct Asian giant hornets to the wrong place using just the right chemical message.

Insects commonly use pheromones to tell one sex (typically males) where to find the opposite sex for mating purposes. Dots in the image represent a pheromone plume released by a female that alerts the male of her presence. Infographic credit: Bug Lessons Consulting LLC

​Scientists in the field of chemical ecology study the chemical interactions among and between living organisms and their environment. For instance, pheromones are important chemicals that animals use to communicate with one another. Popular media often presents pheromones as mysterious chemicals that attract the opposite sex, even though to date, scientists have not identified a single human pheromone. However, pheromones are not just chemicals that lure in a romantic partner. 
 
Technically speaking, pheromones are chemical messages between individuals of the same species that cause a very specific reaction, like a change in behavior. In fact, there are eight types of pheromones used by insects, and experts classify them based on the behavior triggered (e.g., aggregation, alarm, home recognition, and sex pheromones).

Companies often market colognes, especially those for men, to sound like they contain pheromones that are attractive to women. However, scientists have not identified any human-specific sex pheromones. Some movies, like Anchorman, have parodied this phenomenon. Photo credit: memedroid.com, CaptainEnglish, https://www.memedroid.com/memes/detail/109240)

​CAN PEOPLE USE PHERMONES TO CONTROL BUGS?
 
Researchers can identify some of the chemical messages that insects send to one another. Sometimes, the results can be used to artificially replicate the messages to trick insects into traps. People have used pheromones against insects for a while now. However, pheromones as part of a management program are not always practical. 
 
Pheromone identification is a complex and expensive process. Also, professionals and consumers can typically only use pheromone products against one pest at a time because these compounds are species-specific. In spite of these potential setbacks, insect traps that use pheromones have been developed for pests like bed bugs, moths, and carpet beetles. Now, scientists have a lead on the necessary components to attract Asian giant hornets. 

​​There has been a lot of media coverage on the Asian giant hornet (Vespa mandarinia) since its invasion into the Pacific northwest in 2019. Popularly called “murder hornets”, the species has caused widespread panic that they are going to hurt people. Fortunately, these hornets pose little direct threat to folks. Unfortunately, there is real concern that the species might establish in the United States. To try to avoid this, there has been a frenzy on the part of researchers to eliminate them from North America.

​In March of this year, researchers identified three important components of the sex pheromone that female Asian giant hornets release to attract males. Although the “real stuff” released from a live queen attracts more males than the stuff created by scientists, sticky traps laced with the synthetic blend captured thousands of males in the field.
 
This year, scientists will set thousands of traps to monitor for invasive Asian giant hornets in the Pacific northwest. These traps do not contain the recently identified components of the Asian giant hornet sex pheromone. However, in the future, researchers believe that adding the blend to traps could increase the capture success and reduce the number of traps necessary for monitoring efforts. In other words, save time and money! 

Asian giant hornets (Vespa mandarina) are much larger than native hornet species in the United States. They are commonly confused with European hornets (Vespa crabo), the only true hornet found in North America. Photo credit: Washington State Department of Agriculture

On that note, people generally use traps to monitor presence and number of pests rather than controlling insect populations. For example, since female Asian giant hornets are responsible for egg-laying and colony production, only capturing males might not reduce the number of hornets if they already mated with a female prior to capture. However, capturing males would help scientists quickly detect overall hornet activity. Thus, pest managers can use pheromone traps in the “identification” and “monitoring” portions of an integrated pest management plan. 
 
FINAL THOUGHTS
 
Chemical ecology can help develop products that protect many different environments from pests. For instance, constantly monitoring for insect activity may stop invasive species from infesting by detecting invaders sooner rather than later. In field crops and forests, pheromone traps have been instrumental in reducing damage to plants. Additionally, these types of products are used in structures to monitor activity of urban and stored product pests. Only by listening and deciphering the secret messages of insects can we use their languages against them.

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