DOI: 10.5061/dryad.xd2547dn6
title: Evolution of wing scales in the Diptera

description: 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.
description: All studied specimens are deposited in public institutions.
 The study was based on an inclusion in
 Baltic amber (age: Eocene,
 Lutetian–Priabonian;
 Grimaldi and Ross 2017) from the private collection of Christel Hoffeins
 and Hans Werner Hoffeins. The holotype described herein is deposited in
 the Senckenberg Deutsches Entomologisches Institut (SDEI), Müncheberg,
 Germany. Comparative recent specimens: <em>Maietta
 trimedia</em> Alexander, 1967, Chile, Aysen, 25 km S of Cochuane,
 1-2.02.1990, coll. L. E. Peña (housed in ISEA PAS), and the specimens
 listed in  Santos et al. (2019). 
 <strong>Methods</strong>
 The specimens were examined
 with a Nikon (SMZ25) stereomicroscope equipped with a Nikon digital camera
 (DS-Ri2) at the ISEA PAS. Photographs and drawings were made using a Nikon
 SMZ 1500 stereomicroscope equipped with a Nikon DS–Fi1 camera at the
 University of Rzeszów. Usually, 10-30 stacked photographs were combined
 using Helicon Focus 5.3x64 (Helicon Soft Ltd (c)
 2013). The measurements were taken with
 NIS–Elements D 3.0 software. Drawings were completed by tracing the
 photographs. The wing venation nomenclature follows Krzemiński and
 Krzemińska (2003) and the terminology of male genitalia is according to
 Alexander and Byers (1981). Some
 structures of <em>Maietta (Maietta) trimedia</em> Alexander,
 and a mosquito, <em>Ochlerotatus</em> sp., were analyzed under
 the scanning microscope Hitachi SU 8010 SEM at the Podkarpacie Innovative
 Research Center of the Environment (PIRCE) at the University of Rzeszów.
 For scanning electron microscope (SEM) observations, specimens were
 attached to aluminum stubs and sputtered with 20 nm of gold using a
 Turbo-Pumped Sputter Coater Quorum Q 150OT ES.
description: The article is descriptive, illustrated with 7 plates of drawings
 and photos and one table (Table 1). The Table 1 is created based on
 references, as listed in this table.There are three supplementary files:
 1. morphology of the recent and fossil species of Maietta; 2. Phylogeny of
 the genus Maietta; 3. Climate in Eocene and now in localities of fossil
 and recent Maietta. No codes and special abbreviations are used.