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Antennae sense frequency of wing beats: mosquito

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The fine hair-like structures on the antennae of male mosquitos aid in them finding females. This image was taken with EVO® MA10. / ZEISS Micros.. / LicenseCC-by-nc-nd - Attribution Non-commercial No Derivatives

The antennae of male mosquitoes help them find female mosquitoes by sensing the frequency of their wing beats with fine, hair-like structures.

BIOMIMICRY TAXONOMY
Summary
Antenna are non-visionary sensory organs found in many insects. Mosquitoes uniquely utilize their antennas for auditory sensing, otherwise known as hearing. Insects generally have one of two types of auditory sensing, one that responds to the pressure fluctuations and one that responds to movement of air particles. Mosquitoes utilize their antennas as movement receivers, which respond to oscillations of air particles within the mosquitoes surroundings.  Male mosquitoes, in specific,  have adapted their antennas ability to detect sound as a tool to locate female mosquitoes for mating. The anatomy of male mosquitoes antenna allows them to specifically recognize the frequency of female mosquitoes wing beat while flying. 
 
Structurally mosquitoes have two antenna, located beneath their eyes, that each have two segments - the primary and secondary segment. The primary segment is composed of a shaft that, in male mosquitoes, are plumose, meaning they are coated in long feather-like fibrils or hairs. These hairs are shorter at the tip of the shaft and increase in length towards to rear end of the shaft.The primary segment is connected directly to the secondary segment which holds the Johnston organ. The Johnston organ is a spherical base that is densely packed with neuronal sensory receptors. This bundle of sensory receptors are extra sensitive to the forces that act on the hairs of the shaft. When the hairs are moved, the forces are almost immediately transmitted and recognized by the sensitive neurons in the Johnston organ.
 
Sounds create oscillating waves, or in other words, vibrations. Depending on the frequency of sound around a mosquito, these oscillating waves emit forces (higher frequencies create stronger forces, lower frequencies create weaker forces). It is thought that the hairs and the shaft of male mosquitoes antenna are extremely well coupled with the frequency of female wing beats. When male mosquitoes are within a few centimeters of female mosquitoes, the oscillations of air particles (also vibrations, or, sound waves) from the female flight sound cause the hairs on the males antenna to displace in a particular way. At the biological frequency of female mosquito’s wing beat this displacement occurs in phase with the displacement of the antenna shaft (aiding in an even stronger sensory signal). Having this coupling increases the acoustic sensitivity of the harmonic oscillations, allowing the signal to be transmitted to the sensitive Johnston organ. 
 
Female flight sound been measured at roughly 380 Hz. When using a tuning fork at this frequency, male mosquitoes are drawn to the tuning fork. This indicates that the sound, and its vibrational waves patterns, is the primary sensory mechanism for male mosquitos. As discussed earlier, every frequency emits a different type of wave pattern; 380 Hz and its coupled wave pattern are indicative that a female mosquito is near by and thus, aid in efficient recognition for reproductive purposes.

This summary was contributed by Sarah Dodge.
Excerpt
"The antennae of male mosquitoes and midges are also adapted to find females of their kind, but in a different way. The brush-like male antennae are sensitive to sound waves, particularly to those of the frequency of the wingbeat of females; so when a male midge 'hears' a female with his antennae, he flies towards the source of the good vibrations. The response is so simple that the insect will be attracted to anything producing vibrations at the correct frequency (even a tuning-fork)…" (Foy and Oxford Scientific Films 1982:133)

"The antennae of male mosquitoes demonstrate obvious structural modifications that are absent from the antennae of females. In addition to differences in the structure of Johnston’s organ proper, the flagellum of the male antenna is plumose, bearing whorls of extremely long and thin flagellar sensory hairs (also called fibrils). Since the length of these hairs decreases continuously towards the antennal tip, the shape of the male mosquito antenna is reminiscent of a Christmas tree. It has been proposed that antennal hairs are a prerequisite for acoustic sensitivity since, in the males of some mosquito species, for which acoustic communication could not be demonstrated, such antennal anatomy is absent." (Gopfert 1991: 2727-28)
 
 "The fact that the antennal hairs resonate at higher frequencies only indicates that they are stiffly coupled to the shaft. Experimentally, this is illustrated by the fact that the hairs vibrate relative to the shaft only when stimulated at frequencies above 1000 Hz. When stimulated at biologically relevant frequencies (350–500 Hz), the hairs undergo a displacement that is in phase with that of the shaft, suggesting that the biologically significant mechanical property of the hairs is to provide a stiff coupling between the vibrations of the hairs and those of the shaft. In this way, forces acting on the hairs are effectively transmitted to the shaft and therefore to Johnston’s organ." (Gopfert 1991: 2737)
 
About the inspiring organism
Culicidae
Culicidae

Learn more at EOL.org
Organism/taxonomy data provided by:
Species 2000 & ITIS Catalogue of Life: 2008 Annual Checklist


Bioinspired products and application ideas

Application Ideas: Traps or insecticides that employ frequencies that mimic the wingbeats of female mosquitoes, biological pest controls.

Industrial Sector(s) interested in this strategy: Public health, Agriculture

References
Foy, Sally; Oxford Scientific Films. 1982. The Grand Design: Form and Colour in Animals. Lingfield, Surrey, U.K.: BLA Publishing Limited for J.M.Dent & Sons Ltd, Aldine House, London. 238 p.
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Gopfert M.C; Briegel H; Robert D. 1999. Mosquito Hearing: Sound-Induced Antennal Vibrations in Male and Female Aedes Aegypti. The Journal of Experimental Biology. 202: 2727-2738.
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