Living With Cornicles

Red Aphids

Red Aphids on a Cup Plant.
Note black cornicles on abdomen

Cornicles are prominent structures on the abdomens of aphids. The short tubes rise above the body of the aphid. Historically, there was much confusion in the literature about the function of cornicles. It was erroneously assumed that cornicles released honeydew. The assumption that cornicles released honeydew persisted even after it had been demonstrated that honeydew was secreted from the digestive system.

Difficulty in assigning a role to secretions of the cornices was in part due to the inability to analyzes the droplet contents. It was not until after the invention of GC-MS (gas chromatography – mass spectroscopy) that secretion components were identified and misconceptions put to rest.

A.F.G. Dixon was one of the first to propose a defensive function in 1958. A 1967 paper published in the journal Nature, “Defense by Smear” by John S Edwards more fully described a defensive function of cornice secretions. Edwards had collected aphids from the field with parasitoids stuck to the cornices. In laboratory observations, he noted that poking and aphid would induce it to release a droplet form the cornicle on the side that the poke was received. He found that droplets collected from aphids quickly crystallized. The droplets were capable of immobilizing predators.

Edward’s paper stirred a flurry of research into aphid secretions. These investigations found no evidence of honeydew secretion. Instead they uncovered a variety of lipids that differed among aphid species and led to the identification of aphid alarm pheromones, chemicals that cause aphids to cease feeding and drop from the plant. Today we understand cornicles as primarily defensive organs that produce lipids and alarm pheromones.

*J.S. EDWARDS. 1966. Defense by smear: supercooling in the cornicle wax of aphids. Nature, Lond. 211, 73-74.

About jjneal

Jonathan Neal is an Associate Professor of Entomology at Purdue University and author of the textbook, Living With Insects (2010). This blog is a forum to communicate about the intersection of insects with people and policy. This is a personal blog. The opinions and materials posted here are those of the author and are in no way connected with those of my employer.
This entry was posted in behavior, Biomaterials, by jjneal, Environment. Bookmark the permalink.

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