Pheromones

From Chempedia

Pheromones are molecular substances that transmit chemical messages between organisms of the same species. Individuals release pheromones that cause behavioral or physiological changes in other individuals of the same species. Many types of organisms use pheromones to communicate, but the greatest number of characterized pheromones comes from insect species. Social insects that live in colonies, like bees and ants, use pheromones to coordinate activities that are needed to maintain a thriving colony.[1] Every species has its own unique blend of pheromones that are only received by members of the same species. Pheromones have a specific size and structure that allow them to send and convey specific messages to members of the same species. There are four main categories of pheromones:

  • Sex pheromone – used to attract an individual of the opposite sex for mating purposes
  • Aggregation pheromone – used to swarm insects to a particular site for feeding or mating
  • Alarm pheromone – used to signal danger to others and recruit the soldiers of the colony to attack the enemy
  • Trail pheromone – used to lead others to food and to mark territories[2]

Since most pheromones are transmitted through the air, they tend to be volatile. Volatility is the tendency of a substance to become a gas. Most of these compounds are from one of the following volatile chemical groups:

  1. Hydrocarbons
  2. Alcohols (hydrocarbons with an OH-group)
  3. Ketons (hydrocarbons with an oxygen atom attached via a double bond)
  4. Acetates (hydrocarbons with an OCOCH3- group attached)[3]

These four groups are shown in the respective figures 1, 2, 3 and 4. In chemical terms, these compounds are quite small.

Image:pheromones_1.gif

Figure 1: Hydrocarbon

Image:pheromones_2.gif

Figure 2: Alcohol

Image:pheromones_3.gif

Figure 3: Ketone

Image:phermones_4.gif

Figure 4: Acetate

Pheromones are synthesized in specialized glands. For example, Queen honeybees use enzymes in their body to turn an 18-hyrdocarbon chain into a 10-hydrocarbon chain, and then add a hydroxyl group (OH). Next, an oxygen is added to the hydroxylated chain. The pheromone is then released from the gland through a duct and transmitted through the air signaling worker bees to take care of the queen’s larvae.[4] Alarm pheromones in bees primarily consist of alcohol or acetate groups, but this is not necessarily true for all organisms. Other insects may use alcohol groups for aggregation pheromones, for example. In other words, one type of pheromone does not correlate to one specific chemical group. The presence of the pheromones causes a sensory reaction in the receiving insect through specialized organs, usually antennae. When the pheromone molecule comes in contact with the receiving insect’s sensilla it causes nervous stimulation that sends signals to the brain to invoke a response in the insect’s motor system (see figure 5).[5]

Image:pheromones_5.jpeg

Figure 5: Receiving insect response to pheromone.

Pheromones are an integral part of insect survival, and humans are now finding ways to control insect behavior by creating synthetic pheromones that disrupt normal communication between insects. For example, some farmers are using a technique called "mating disruption". This process consists of releasing a synthetic pheromone from various points throughout the crop. This wide dispersal of pheromones makes it difficult for the males to locate the females, thus reducing the number of matings and offspring.[6] The use of synthetic pheromones to control insect populations is a less harmful alternative to insecticides. Future research on the functions of pheromones relate to new and less harmful methods of pest and disease control. While most research has been done on insect pheromones, there continues to be research on the use of pheromones in other organisms such as fungi, bacteria, and mammals. Research on human pheromones has led scientists to believe that our pheromones are produced by the apocrine glands, which become functional after reaching puberty. This may explain why a person can sense "chemistry" with another person, or feel an instant attraction or dislike for someone upon meeting for the first time.[7]


Adam Larson, LyTou Li, Kevin Nguyen, & Amanda E. Oporto

Chem 1022

Fall 2005

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Footnotes

  1. ^ J. Meinwald, “Pheromone,” in AccessScience@McGraw-Hill, http://www.accessscience.com, DOI 10.1036/1097-8542.506950, last modified: April 10, 2000. (Accessed on 9/22/05)
  2. ^ Russell Jurenka, "Insect physiology", in AccessScience@McGraw-Hill, http://www.accessscience.com, DOI 10.1036/1097-8542.346000, last modified: January 16, 2002.
  3. ^ “The Wonderful World of Pheromones” – Chemistry, http://hangmat.etv.cx/chemEN.html. (Accessed on 9/22/05)
  4. ^ Adler, T., “How the Queen Bee Makes Her Pheromone,” Science News, 1996, 194 (13), p198.
  5. ^ Leal, Walter S., “Pheromone Reception”, in The Chemistry of Pheromones and Other Semiochemicals II, ed. Stephen Schulz, Springer-Verlag: Berlin, 2005;pp3.
  6. ^  Fluri, P., Mani, E., Wildbolz, T. & Arn, H. “About Pheromones”, http://www.nysaes.cornell.edu/pheronet/pherom.html. (Accessed on 9/22/05)
  7. ^ Pheromone, http://en.wikipedia.org/wiki/Pheromone. (Accessed on 9/22/05)
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