Brochosome

Microscopic granules secreted by leafhoppers

Brochosomes are intricately structured microscopic granules secreted by leafhoppers (the family Cicadellidae of the insect order Hemiptera) and typically found on their body surface and, more rarely, eggs. Brochosomes were first described in 1952 with the aid of an electron microscope. Brochosomes are hydrophobic and help keep the insect cuticle clean. These particles have also been found in samples of air and can easily contaminate foreign objects, which explains erroneous reports of brochosomes on other insects. The name, derived from the Greek words βρóχoς ("brochos": mesh of a net) and σωμα ("soma": body), refers to the characteristic reticulated surface of the granules.

Most species of leafhoppers produce hollow spherical brochosomes, 0.2–0.7 micrometres in diameter, with a honeycombed outer wall. They often consist of 20 hexagonal and 12 pentagonal cells, making the outline of each brochosome approximating a truncated icosahedron – the geometry of a soccer ball and a C60 buckminsterfullerene molecule. The chemical composition of brochosomes includes several kinds of proteins and, according to some studies, lipids. The main protein family, called brochosomins, and other kinds of proteins identified in the composition of brochosomes and their corresponding genes show no relationship to proteins and genes of any organisms outside of Membracoidea and thus are considered to be examples of orphan genes.

After each molt, most leafhopper species release droplets of the brochosome containing fluid through the anus and actively spread them over the newly formed integument. This behavior is called anointing. the latter often being sugary and sticky, and thus potentially dangerous for the insect. Additional protective functions of the brochosomal coating have been hypothesized. In several New World genera of the leafhopper subfamily Cicadellinae (including the glassy winged sharpshooter and related species) brochosomes are also used as a coating on egg masses. In gravid females from these genera, the Malpighian tubules switch over The shape and sculpture of such "egg" brochosomes can vary significantly among species, providing additional characteristics for species identification.