Wait...What's That Smell?

By Anonymous -
We all have those scents that have the power to send us back in time to specific place, person, or memory. Our sense of smell is very powerful, and has been scientifically linked to our ability to remember; yet even though our connection with our noses is an incredible feat, it pales in comparison to the ability of insects to communicate through smells.

Insects rely heavily on chemicals for communication due to their small size. Trying to send a signal a long distance or across certain geographical barriers via other methods would be extremely difficult.
The study of animals’ chemical communication is called chemical ecology, and encompasses a vast array of topics; in this blog I will focus on the difference between two of the types of chemicals insects utilize: pheromones and allelochemicals.

Honey Bee Hive
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Pheromones are chemical substances that are excreted by an individual in order to communicate with its own species. To an average person, pheromones are most often associated with mating, but they can also be used to communicate distress, or a “fight-or-flight” response. This chemical is subdivided into two different categories – primer pheromones and releaser pheromones.  Primer pheromones are scents that have a long-term physiological effect on the receiver, with the most known example being the mandibular pheromone of a honey bee queen. In this example, the queen excretes a chemical consisting of a mix of two fatty acids (see picture), which “suppress[es] ovary development in worker bees” (Reinhard, 2004), allowing the queen to be solely capable of producing eggs. Primer pheromones are also the mode of communication used in social colonies to determine the different castes of the individuals (such as with ants and termites). The other type of pheromone is known as a “releaser pheromone,” which immediately effects the receiver and causes a short-term response rather than a total physiological change. This type of chemical communication is further subdivided by the function they serve, such as a sex pheromone (to attract mates), an alarm pheromone (to warn others of a potential predator) or an aggregation pheromone (to attract others to a specific location).
[You can read a more in depth explanation of these types of pheromones here]

Marmorated Stink Bug
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Allelochemicals are types of chemical signals that are used for communication between different species. This class of chemical communication is divided into three different categories: kairomones, allomones, and synomones. A kairomone is a signal in which the individual, or species, who intercepts the signal benefits from it, but the sender of the signal does not. Predatory insects sometime utilize these signals to locate their prey. On the flip side, allomones are signals that benefit the sender, but not the receiver. Stink bugs use allomones to deter predators from eating them by producing a repugnant odor and a nasty taste. Allomones can also be used by predators, to lure unsuspecting individuals to them (e.g. bolas spiders can make a pheromone that will attract males of a particular moth species to them as a source of food). The third type of allelochemical is the synomone, in which both the sender and the receiver benefit from the signal (sometimes unintentionally).


All of these signals are detected in the air by the olfactory receptors in an insects’ antennae (they are all gaseous chemicals), but insects can also detect and decode chemical signals that are not in the air, but are “in solution” (Baldwyn). Another amazing fact about chemical signaling is that the signal changes depending on the dosage, size, and structure of the chemical compound, and the same signal can act as a repellent and attractant to different species.
[If you would like to read more about chemical receptors and how the different chemicals are interpreted, click here]
https://www.google.com/url?sa=i&rct=j&q=&esrc=s&source=images&cd=&ved=0ahUKEwiV5tDeip7UAhVH1oMKHdl6CRkQ
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 Sources:

Raguso, Robert A. et al. “The raison d’e^tre of Chemical Ecology.” Ecology 96(3). 2015. 617-30. Web. 1 June 2017.

Reinhard, Judith. “Insect Chemical Communication.” ChemoSense, vol. 6, no. 4, 2004. Web. 1 June 2017. <http://www.inscent.com/docs/chemosept04v5.pdf>

Dr. Torto, Baldwyn. “Chemical Signals as Attractants, Repellents and Aggregation Stimulants.” Encyclopedia of Life Support Systems (EOLSS). UNESCO-EOLSS. Eolss.net. Web. 1 June 2017. <http://www.eolss.net/sample-chapters/c06/e6-52-03-05.pdf>


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