Chair of Forest Zoology and Entomology, Albert-Ludwigs-Universität Freiburg i.Br. Chair of Forest Zoology and Entomology
Albert-Ludwigs-Universität Freiburg i.Br.

Chair of Forest Zoology and Entomology
Freiburg i.Br.

Crystal Macrosetae

Boppré M, Fischer OW, Freitag H, Kiesel A (2019) "Crystal macrosetae": novel scales and bristles in male arctiine moths (Lepidoptera: Erebidae: Arctiinae) filled with crystallising material. J Insect Sci: in press

Scales, exoskeletal features characteristic of the Lepidoptera, occur in enormous structural and functional diversity. They cover the wing membranes and other body parts and give butterflies and moths their often stunning appearance. Generally, the patterns made by scales are visual signals for intra- and inter-specific communication. In males scales and / or bristles also make up the androconial organs which emit volatile signals during courtship. Here, a structurally and putative functionally novel type of scales and bristles is reported: "crystal macrosetae". These lack trabeculae and windows, are made up by a very thin and flexible envelope only and contain crystallising material. In "crystal scales" there is a flat surface ornamentation of modified ridges, while "crystal bristles" often show large protrusions. Crystal macrosetae usually cannot be reliably recognised without destruction. Apparently they serve as containers for large amounts of material that is viscous in living moths, highly hygroscopic, crystallises when specimens dry up, and can be visualised by scanning electron microscopy. Crystal macrosetae occur in males only, always associated with or making up androconial organs located on various parts of the body, and have numerous forms with diverse surface ornamentation across many species and genera. The newly identified structures and the discovery of crystallising material in scales and bristles raise many questions and could shed new light on ontogenetic development of macrosetae, and on the biology and physiology as well as the evolution and systematics of Arctiinae. There is evidence that crystal macrosetae occur in other moths too.