So, folks have known for quite a while about the thin-film multilayer reflector mechanism behind interference colors in beetles. H. E. Hinton also described spectral iridescence from microscopic surface gratings in Coleoptera, including some wonderful SEMS of the variety of diffracting mechanisms in Scarabaeidae, Carabidae, and Staphylinidae.
In a recent description of new leiodid species, Dr. Q. D. Wheeler and I (2004) included SEMs of the dorsal face of the elytron. These micrographs reveal an array of tiny raised ridges running parallel to the long axis of the body; under direct illumination with white or natural light, this structure gives rise to laterally displaced high-order spectra. To our knowledge this is the first record of a long-axis diffraction grating in Coleoptera.
Subsequent surveys of museum holdings have revealed that a number of other little-known beetle families (including Nitidulidae, Hydrophilidae, and Mordellidae) also possess dorsal diffraction gratings. Some have been modified in previously undescribed ways, giving rise to an assortment of iridescent effects and curiously modified spectra. I am currently investigating these microscopic structures and their optical effects through photographic and SEM analyses.
TALKS & POSTERS
Spectral iridescence in Coleoptera: optical mechanisms and evolutionary significance. (poster) Section 9, Chemical and Physical Ecology and Behavior.International Congress of Entomology Aug. 2004.
Diffraction gratings in Coleoptera: The mechanism and distribution of unusual structural colors. (talk) Student Competition Ten-Minute Papers, A2. Systematics, Morphology and Evolution. Annual Meeting of the Entomological Society of America, Nov. 2004.
Spectral iridescence in Coleoptera: Optical mechanisms and evolutionary significance. (poster) Poster Session I-- Adaptation. Evolution 2005, Fairbanks AK June 10-14.
For a montage of beetle spectra, click here. (large file).
SEMS and spectra here. (color photos and most SEMs are mine)
A. Seago 2004