What’s in a cornicle? A survival kit for aphids – here’s why. Aphids are extremely successful pests. They love nothing better than vegetable gardens and flower beds where they drain a plant’s energy, transmit viruses, and excrete honeydew on which the growth of sooty mold takes hold. On top of this they reproduce very quickly and they’re great communicators.
Aphids have a way to defend themselves against predation. Their cornicles are the weapon of choice. Cornicles are paired tube-like structures on the fifth or sixth abdomen segment that appear like small exhaust pipes. They can vary in shape, size, length, and color but are a characteristic that all aphids share.
These ‘exhaust pipes’ secrete droplets of fluid when the aphid contracts tiny abdomen muscles located under the cornicle. Scientists thought this liquid was honeydew, but it is in fact a liquid containing lipids, hemolymph, and a substance called an alarm pheromone.
Alarm pheromones function as a type of ‘emergency broadcast system’ given off when there’s a predator nearby. Once a member of an aphid group detects the pheromone, it will stop feeding and walk or fall off the leaf it’s on. Not only that, but some aphids smear the predator before dying, making the predator’s movements detectable by all other aphids. This gives the aphids time to escape – cute.
This production of an alarm pheromone by aphids is an adaptation to counterbalance their tastiness to predators. It’s a tough out there being small but with defensive mechanisms like these aphids are sure to survive!
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