Pheromones

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Pheromones are chemicals released by an organism into its environment, enabling it to communicate with other members of its own species


Insect Pheromones

Alarm Pheromone

  • When an ant is disturbed, it can releases a pheromone that attracts other ants and causes an alarm response 
  • High concentrations cause the ants to run about as they work to remedy the disturbance 
  • Unless additional amounts of the alarm pheromone are released, it soon dissipates 
  • This ensures that once the emergency is over, the ants return quietly to their former occupations


Trail Pheromone

  • Certain ants lay down a trail pheromone, which will attract and guide other ants to a source, such as food 
  • The trail pheromone evaporates quickly, so the more pheromone that exists on the path, the greater the probability other ants will follow it
  • This ensures that ants always take the shortest route around an obstruction - as more ants can traverse a shorter path in a given time period, the pheromone will accumulate quicker on this path


Ant Paths as Determined by Trail Pheromones


Sex Attractants

  • Hundreds of pheromones are known with which one sex (usually the female) of an insect species attracts its mates 
  • Other species of animal and plant may mimic these sex pheromones for their own survival purposes:
    • One species of spider, Mastophora cornigera, releases a scent that mimic the sex pheromone of the moth species it preys upon
    • A number of orchid species emit a scent that mimics the sex pheromone of female wasps and bees - attracting males for the purpose of pollination 
    • Many types of sex attractants are available commercially for use in insect baiting (used in conjunction with conventional insecticides) 


Mammalian Pheromones

Releaser Pheromones

  • Many mammals (e.g. dogs and cats) deposit chemicals in and around their established "territory" (often released in the urine)
  • As these vaporize, they signal to other members of the species of the presence of the occupant of the territory
  • Domestic rabbit mothers release a mammary pheromone that triggers immediate nursing behavior by their babies (pups) 


Primer Pheromones

  • Rats and mice give off pheromones that elicit mating behavior - however the response is not immediate as it is for the sex attractants of insects 
  • Instead, detection of the pheromone primes the endocrine system of the recipient to make the changes (e.g. ovulation) needed for successful mating


Human Pheromones

  • In human females, two uncharacterised pheromones are secreted from armpits, synchronizes menstrual cycles and ovulation in closely-living groups
  • One pheromone is released prior to ovulation and speeds up the onset of ovulation of those close by 
  • The other pheromone is released after ovulation and delays the onset of ovulation in others, effectively 'synchronizing’ the group