Stable structural color patterns displayed on transparent insect wings.

Color patterns play central roles in the behavior of insects, and are
important traits for taxonomic studies. Here we report striking and
stable structural color patterns—wing interference patterns (WIPs)
—in the transparent wings of small Hymenoptera and Diptera,
patterns that have been largely overlooked by biologists. These extremely
thin wings reflect vivid color patterns caused by thin film
interference. The visibility of these patterns is affected by the way
the insects display their wings against various backgrounds with
different light properties. The specific color sequence displayed
lacks pure red and matches the color vision of most insects, strongly
suggesting that the biological significance of WIPs lies in visual
signaling. Taxon-specific color patterns are formed by uneven
membrane thickness, pigmentation, venation, and hair placement.
The optically refracted pattern is also stabilized by microstructures
of the wing such as membrane corrugations and spherical cell structures
that reinforce the pattern and make it essentially noniridescent
over a large range of light incidences. WIPs can be applied to
map the micromorphology of wings through direct observation
and are useful in several fields of biology. We demonstrate their
usefulness as identification patterns to solve cases of cryptic species
complexes in tiny parasitic wasps, and indicate their potentials
for research on the genetic control of wing development through
direct links between the transregulatory wing landscape and interference
patterns we observe in Drosophila model species. Some
species display sexually dimorphic WIPs, suggesting sexual selection
as one of the driving forces for their evolution.