cornicle

A cornicle is one of a pair of slender, tubular structures located on the posterior abdomen of many aphids and some related insects. They project from the body and vary in length from short to conspicuously elongated. Not all aphids have prominent cornicles, and their presence or absence, as well as their shape, can aid in identifying different species.

The primary function of the cornicles is the production and discharge of defensive substances. When disturbed, aphids may exude droplets or spray from the cornicles that contain alarm pheromones and other compounds that deter predators or parasitoids. The secretions are often waxy or oily and can help protect the insect by signaling danger to nearby aphids or by discouraging antagonists. The exact chemical composition of cornicle secretions differs among species and can be influenced by diet and environment. These secretions can also affect interactions with ants, which commonly attend aphids for honeydew and may respond to cornicle-derived cues.

In taxonomy, the presence, length, and shape of cornicles are useful diagnostic characteristics for identifying aphid species and groups. The term cornicle comes from Latin cornu, meaning horn, with the diminutive suffix -icle, reflecting their horn-like appearance. Outside aphids, related tubular abdominal structures are rare, making cornicles a distinctive feature in the study of aphid anatomy.