Evolution of wing scales in the Diptera

Among the insects with wings clad in scales, the butterflies are most known and show the greatest variety of scales. In the Diptera, only some families or particular genera of two large groups are known to bear scales on wings, i.e., mosquitoes (Culicomorpha) and moth flies (Psychodomorpha). From among another large dipteran group, the crane-flies (Tipulomorpha), the scales on wings are present only in one small genus, Maietta Alexander, now endemic to the southwestern coast of South America. Herewith, we describe the Eocene ancestor of Maietta, embedded in Baltic amber, Maietta (Hoffeinsetta ) christelae, n. subgen., n. sp. This species and its recent congeners document the evolution of scale cover from scarce, restricted only to the anterior portion of the wing, to complete and dense. A similar parallel evolutionary route was previously described in the Culicidae. The fossil representative of Maietta provides also a further example of biogeographical relationships of Baltic fauna with recent congeners distributed today far from Europe. The present finding prompts a discussion on a possible protective role of scales against sticky surfaces of resin and the same proposes an explanation to a question: why some insects are astonishingly rare in fossil resins; a problem unsolved since 19th century.