The term “plastron” was first coined by Brocher in the year 1909 (Gorb 2009) or 1912 (Thorpe 1950), (depending on which source you choose to read). It was defined as simply “a film of gas” (Thorpe 1950). We can now define it more specifically as “an incompressible, thin layer (bubble) of air supported by specialized minute hairs (microtrichia in this case) or alveolar structures […] on the body and in contact with the spiracles (or air exchange structure) of the insect” (Gorb 2009).

Perhaps the first important study of plastrons was performed by Ege, who demonstrated that if the hairs on an insect's surface are sufficiently close together and can avoid becoming wet, then it is possible to form a gas gill that maintains a volume of air against some degree of pressure. The results of Ege’s work were confirmed by Thorpe (Thorpe 1950).

However, the investigations that changed the study of this topic the most dramatically were those of W.H. Thorpe. In his paper published in 1950, Thorpe provided a detailed basis of knowledge about plastrons and compressible gills (Thorpe 1950), from which all other research stemmed.  

As time has gone on and technology has improved, a more in depth study of plastron surfaces and compressible gas gills has become possible. Some of the earlier studies of aquatic insect respiration involved the examination of their surfaces through the use of spectroscopic microscopes (Parsons 1970), but much of the studying of aquatic insect surfaces has been done using a scanning electron microscope (Richards 1979) (Heckman 1983) (Gorb 1997) (Balmert et al 2011) (Goodwyn et al 2008), which gives a much more detailed view of the properties of the setae and microtrichia that allow plastron surfaces and physical gills to be possible.

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Selected air retaining body parts of Notonecta glauca: A,B) setae on the abdominal sternites; C,D) underside of the elytra with a dense cover of microtrichia; E,F) upper side of elytra with a hierarchical double structure of microtrichia and setae. Two different types of setae occur. In all pictures the caudal direction of the insect is on the right side. (Credit: Petra Ditsche-Kuru, Erik S. Schneider, Jan-Erik Melskotte, Martin Brede, Alfred Leder and Wilhelm Barthlott: Superhydrophobic surfaces of the water bug Notonecta glauca: a model for friction reduction and air retention. In: Beilstein J. Nanotechnol. 2011, 2, 137–144.)

Besides visual observations of such surfaces, experiments have also been performed that have made mathematical models of various aspects of plastrons and gas gills possible to construct. Flynn and Bush (2008) derive multiple mathematical models of factors including mechanical stability of the plastrons, the effect of dynamic pressure, and others.

Computer models can also be utilized to explore factors affecting oxygen gain in diving insects and spiders, such as was done by Chaui-Berlinck et al. They performed computer-based simulations of insect dives. Their results indicated that perhaps oxygen gain was not as important a factor as originally believed (Chaui-Berlinck and Bicudo 1993). This use of computer simulations not available in the past thus led to the questioning of the results of previous experiments that indicated that oxygen gain is fixed in gas gills (Chaui-Berlinck et al 2001).However, Matthews and Seymour (2010) performed an investigation that produced results that contradict Chaui-Berlinck et al's conclusions.

Another relatively recent advance in research of plastron surfaces and gas gills relates to its technological and biomimetic implications. Physical models of the plastron have been manufactured and tested (Shirtcliffe et al 2006), and the technological possibilities that this provides are being explored (Shirtcliffe et al 2006) (Flynn and Bush 2008) (Balmert et al 2011). (see Biomimicry: The Plastron's Contribution to Technology)

The copyright holder of this work released this work into the public domain. This applies worldwide. (Credit:HandigeHarry)

One possible technological use of artificial plastrons is to provide oxygen for fuel cells under water (Shirtcliffe et al 2006).