Johnston's organ is a collection of sensory cells found in the pedicel (the second segment) of the antennae in the

class Class or The Class may refer to: Common uses not otherwise categorized * Class (biology), a taxonomic rank * Class (knowledge representation), a collection of individuals or objects * Class (philosophy), an analytical concept used differently ...

Insecta Insects (from Latin ') are pancrustacean hexapod invertebrates of the class Insecta. They are the largest group within the arthropod phylum. Insects have a chitinous exoskeleton, a three-part body (head, thorax and abdomen), three pairs o ...

. Johnston's organ detects motion in the

flagellum A flagellum (; ) is a hairlike appendage that protrudes from certain plant and animal sperm cells, and from a wide range of microorganisms to provide motility. Many protists with flagella are termed as flagellates. A microorganism may have f ...

(third and typically final antennal segment). It consists of scolopidia arrayed in a bowl shape, each of which contains a mechanosensory chordotonal neuron. The number of scolopidia varies between species. In homopterans, the Johnston's organs contain 25 - 79 scolopidia. The presence of Johnston's organ is a defining characteristic which separates the class

from the other hexapods belonging to the group Entognatha. Johnston's organ was named after the physician Christopher Johnston, father of the physician and Assyriologist

Christopher Johnston Christopher Johnston may refer to: * Christopher Johnston (Assyriologist) (1856–1914), American physician and Assyriologist, a scholar of ancient Mesopotamia *Chris Clavin Chris Clavin (born Christopher Johnston; August 23, 1973) is an Ameri ...

Uses of the Johnston's organ

In fruit flies, nonbiting midges and mosquitoes

In the fruit fly ''

Drosophila melanogaster ''Drosophila melanogaster'' is a species of fly (the taxonomic order Diptera) in the family Drosophilidae. The species is often referred to as the fruit fly or lesser fruit fly, or less commonly the " vinegar fly" or "pomace fly". Starting with ...

and

Chironomus annularius ''Chironomus annularius'' (commonly known as bayfly or mufflehead) is a species of non-biting midge in the family Chironomidae. It is usually found in regions with bodies of fresh water but can be found in almost every environment. It tends to fo ...

'', the Johnston's organ contains almost 480 sensory neurons. In the mosquito, the Johnston's organ houses ~15 000 sensory cells in males, comparable to that in the human cochlea, and approximately half as many in females. Distinct populations of neurons are activated differently by deflections of antennae caused by gravity or by vibrations caused by sound or air movement. This differential response allows the fly to distinguish between gravitational, mechanical, and acoustic stimuli. The Johnston's organ of fruit flies, chironomids or mosquitoes can be used to detect air vibrations caused by the wingbeat frequency or courtship song of a mate. One function of the Johnston's organ is for detecting the wing beat frequency of a mate. Production of sound in air results in two energy components: the pressure component, which is changes in air pressure; and the particle displacement component, which is the back and forth vibration of air particles oscillating in the direction of sound propagation. Particle displacement has greater energy loss than the pressure component when getting further from the sound source, so for quiet sounds such as small flies, it is detectable only within a few wavelengths of the source. Insects, such as fruit flies and bees, detect sounds using loosely attached hairs or antennae which vibrate with air particle movement. (Tympanal organs detect the pressure component of sound.) Near-field sound, because of the rapid dissipation of energy, is suitable only for very close communication. Two examples of near-field sound communication are bee's waggle dance and ''Drosophila'' courtship songs. In fruit flies, the arista of the antennae and the third segment act as the sound receiver. Vibrations of the receiver cause rotation of the third segment, which channels sound input to the mechanoreceptors of the Johnston's organ.

In hawk moths

The Johnston's organ plays a role in the control of flight stability in hawk moths. Kinematic data measured from hovering moths during steady flight indicate that the antennae vibrate with a frequency matching wingbeat (27 Hz). During complex flight, however, angular changes of the flying moth cause Coriolis forces, which are predicted to manifest as a vibration of the antenna of at about twice wingbeat frequency (~60 Hz). When antennae were manipulated to vibrate at a range of frequencies and the resulting signals from the neurons associated with the Johnston's organs were measured, the response of the scolopidia neurons to the frequency was tightly coupled in the range of 50–70 Hz, which is the predicted range of vibrations caused by Coriolis effects. Thus, the Johnston's organ is tuned to detect angular changes during maneuvering in complex flight.

In honeybees

Dancing honeybees (''

Apis mellifera The western honey bee or European honey bee (''Apis mellifera'') is the most common of the 7–12 species of honey bees worldwide. The genus name ''Apis'' is Latin for "bee", and ''mellifera'' is the Latin for "honey-bearing" or "honey carrying", ...

'') describe the location of nearby food sources by emitted airborne sound signals. These signals consist of rhythmic high-velocity movement of air particles. These near-field sounds are received and interpreted using the Johnston's organ in the pedicel of the antennae.

Honeybees A honey bee (also spelled honeybee) is a eusocial flying insect within the genus ''Apis'' of the bee clade, all native to Afro-Eurasia. After bees spread naturally throughout Africa and Eurasia, humans became responsible for the current c ...

also perceive electric field changes via the Johnston's organs in their antennae and possibly other mechanoreceptors. Electric fields generated by movements of the wings cause displacements of the antennae based on

Coulomb's law Coulomb's inverse-square law, or simply Coulomb's law, is an experimental law of physics that quantifies the amount of force between two stationary, electrically charged particles. The electric force between charged bodies at rest is convention ...

. Neurons of the Johnston's organ respond to movements within the range of displacements caused by electric fields. When the antennae were prevented from moving at the joints containing the Johnston's organ, bees no longer responded to biologically relevant electric fields. Honeybees respond differently to different temporal patterns. Honeybees appear to use the electric field emanating from the dancing bee for distance communication.

References

{{reflist Insect anatomy Sensory organs in animals