Johnston's organ

Definition

A chordotonal mechanosensory organ located in the pedicel (second antennal segment) of insects, consisting of an array of scolopidia that detect movement and vibration of the flagellum. The organ functions in proprioception, wind detection, sound reception (especially near-field sounds in some groups), and gravity sensing. Its presence is a diagnostic synapomorphy distinguishing Insecta from Entognatha.

Etymology

Named for Christopher Johnston (1822–1891), American physician.

Example

Male mosquitoes use their enlarged Johnston's organs to detect the wing-beat frequencies of females during mating swarms; Drosophila employs the organ for gravity sensing and rapid turning responses during flight.

Synonyms

• Johnston organ

Related Terms

• scolopidium
• Chordotonal organ
• Pedicel
• Flagellum
• mechanoreceptor
• proprioception
• tympanal organ
• antenna

Usage Notes

The organ's sensitivity varies dramatically with flagellum length and scolopidium number—honey bees possess ~300 scolopidia while some small flies have fewer than 50. In Diptera, the organ is often hypertrophied and associated with sexual selection through acoustic detection. The term is sometimes written without the possessive apostrophe ("Johnston organ") in modern literature, though the eponymous form remains standard.