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5 Pheromones
Key Idea: A pheromone is a chemical produced by an animal and released into the external environment where it affects the physiology or behaviour of members of the same species. Pheromones, which are often sex attractants, are common amongst insects and mammals, and commonly relate to reproductive behaviour. Many mammals, including canids and all members of the cat family, use scent marking to mark territories and advertise their readiness to mate. Other mammals, including rabbits, release a mammary pheromone that triggers nursing behaviour in the young. Pheromones are also used as signalling molecules in social insects such as bees, wasps, and ants. They may be used to mark a scent trail to a food source or to signal alarm. Pheromones are widely used as baits to attract and trap insect pests.
Pheromones produced by a honey bee queen and her daughters, the workers, maintain the social order of the colony. The pheromone is a blend of unsaturated fatty acids. In mammals, pheromones are used to signal sexual receptivity and territory, or to synchronise group behaviour. Pheromone detection relies on the vomeronasal organ (VNO), an area of receptor tissue in the nasal cavity. Mammals use a flehmen response, in which the upper lip is curled up, to better expose the VNO to the chemicals of interest.
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Reptiles also use the VNO to detect chemicals. The flicking of a snake's tongue samples chemicals in the environment and delivers them to the VNO. This behaviour is used to detect prey.
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Communication in ants and other social insects occurs through pheromones. Foraging ants leave a trail along the ground that other ants will follow and reinforce until the food source is depleted. Ants also release alarm substances, which will send other ants in the vicinity into an attack frenzy. These signals dissipate rapidly if not reinforced. The feathery antennae of male moths are specialised to detect the pheromone released by females. Males can detect concentrations as low as 2 ppm. They use wind direction to orientate, flying upwind to find the female. The sex attractant property of pheromones is used in traps, which are widely used to trap insect pests in orchards.
1. (a) What is a pheromone?
(b) What is the significance of pheromones being species specific?
2. Explain how the response of a male moth to female pheromone is adaptive:
3. Explain the role of pheromones in orientation and communication in social insects:
