from C. T. Bingham (1905) Some claim insects evolved from prehistoric crustaceans, and they have secondary antennae like crustaceans, but not primary antennae. Antennae are the primary
olfactory sensors of insects and are accordingly well-equipped with a wide variety of
sensilla (singular:
sensillum). Paired, mobile, and segmented, they are located between the eyes on the forehead. Embryologically, they represent the appendages of the second head segment. All insects have antennae, however they may be greatly reduced in the larval forms. Amongst the non-insect classes of the
Hexapoda, both
Collembola and
Diplura have antenna, but
Protura do not. Antennal fibrillae play an important role in
Culex pipiens mating practices. The erection of these fibrillae is considered to be the first stage in reproduction. These fibrillae serve different functions across the sexes. As antennal fibrillae are used by female
C. pipiens to locate hosts to feed on, male
C. pipiens utilize them to locate female mates.
Structure of antenna surface detail of a wasp
(Vespula vulgaris) The three basic segments of the typical insect antenna are the
scape or
scapus (base), the
pedicel or
pedicellus (stem), and finally the
flagellum, which often comprises many units known as
flagellomeres. The pedicel (the second segment) contains the
Johnston's organ which is a collection of sensory cells. The scape is mounted in a socket in a more or less ring-shaped
sclerotised region called the
torulus, often a raised portion of the insect's head capsule. The socket is closed off by the membrane into which the base of the scape is set. However, the antenna does not hang free on the membrane, but pivots on a rigidly sprung projection from the rim of the torulus. That projection on which the antenna pivots is called the
antennifer. The whole structure enables the insect to move the antenna as a whole by applying internal muscles connected to the scape. The pedicel is flexibly connected to the
distal end of the scape and its movements in turn can be controlled by muscular connections between the scape and pedicel. The number of flagellomeres can vary greatly between insect species, and often is of diagnostic importance. True flagellomeres are connected by membranous
linkage that permits movement, though the flagellum of "true" insects does not have any
intrinsic muscles. Some other
Arthropoda do however have intrinsic muscles throughout the flagellum. Such groups include the
Symphyla,
Collembola and
Diplura. In many true insects, especially the more primitive groups such as
Thysanura and
Blattodea, the flagellum partly or entirely consists of a flexibly connected string of small ring-shaped
annuli. The annuli are not true flagellomeres, and in a given insect species the number of annuli generally is not as consistent as the number of flagellomeres in most species. In the groups with more uniform antennae, all segments are called
antennomeres. Some groups have a simple or variously modified apical or subapical bristle called an
arista (this may be especially well-developed in various
Diptera).
Functions '', electron micrograph
Olfactory receptors on the antennae bind to free-floating molecules, such as
water vapour, and
odours including
pheromones. The
neurons that possess these receptors signal this binding by sending
action potentials down their
axons to the
antennal lobe in the
brain. From there, neurons in the antennal lobes connect to
mushroom bodies that identify the odour. The sum of the electrical potentials of the antennae to a given odour can be measured using an
electroantennogram. In the
monarch butterfly, antennae are necessary for proper time-compensated
solar compass orientation during migration. Antennal clocks exist in monarchs, and they are likely to provide the primary timing mechanism for sun compass orientation. In the
African cotton leafworm, antennae have an important function in signaling courtship. Specifically, antennae are required for males to answer the female mating call. Although females do not require antennae for mating, a mating that resulted from a female without antennae was abnormal. In the
diamondback moth, antennae serve to gather information about a host plant's taste and odor. After the desired taste and odor has been identified, the female moth will deposit her eggs onto the plant.
Giant swallowtail butterflies also rely on antenna sensitivity to volatile compounds to identify host plants. It was found that females are actually more responsive with their antenna sensing, most likely because they are responsible for oviposition on the correct plant. In the crepuscular hawk moth (
Manduca sexta), antennae aid in flight stabilization. Similar to
halteres in Dipteran insects, the antennae transmit
coriolis forces through the Johnston's organ that can then be used for corrective behavior. A series of low-light, flight stability studies in which moths with flagellae amputated near the pedicel showed significantly decreased flight stability over those with intact antennae. To determine whether there may be other antennal sensory inputs, a second group of moths had their antennae amputated and then re-attached, before being tested in the same stability study. These moths showed slightly decreased performance from intact moths, indicating there are possibly other sensory inputs used in flight stabilization. Re-amputation of the antennae caused a drastic decrease in flight stability to match that of the first amputated group. ==References==