Another species of Palaeoglaesum (Diptera, Psychodidae, Bruchomyiinae) from mid-Cretaceous Kachin amber

Abstract

Bruchomyiinae is a small subfamily of moth flies (Psychodidae) which includes fewer than 60 species restricted to tropical and subtropical regions (Curler & Jacobson, 2012; Wagner & Stuckenberg, 2016; Wagner, 2017; Skibińska & Santos, 2023). Despite their low species diversity, representatives of this subfamily are relatively common in the fossil record. To date, 28 fossil species across five genera have been identified. All known fossil representatives are preserved as inclusions in various fossil resins, ranging in age from Lower Cretaceous Lebanese amber (Azar et al., 2022) to Lower Miocene Dominican amber (Wagner, 2017). The genus Palaeoglaesum Wagner, 2017 is an extinct taxon known exclusively from Kachin amber, Myanmar. This genus comprises 15 species distributed in two subgenera: Palaeoglaesum (Palaeoglaesum) and Palaeoglaesum (Amplissimum) (Skibińska & Santos, 2023). This genus is the most diverse fossil representative of this subfamily. Diagnostic characters of Palaeoglaesum include a small body size (approximately 2‒2.5 mm), dense setation, a head with a median longitudinal strip of setae, elongate mouthparts with prominent labellum, and an oval wing with a broadly rounded apex. The vein R₂₊₃ is at least twice as long as R₂, and the radial fork is positioned distally to the medial fork. Male genitalia exhibit either an elongated, apically bifurcated aedeagus or a short, non-bifurcated form, both surrounded at the base by a sleeve-like parameral sheath (Skibińska et al., 2021; Skibińska & Santos, 2023). The high number of Palaeoglaesum species found in Kachin amber suggests that the tropical, near-coastal climate of the mid-Cretaceous Myanmar amber forest provided favorable conditions for a high diversity of Bruchomyiinae. Their ecology is closely associated with forest habitat, particularly tree hollows, forest litter, and tree trunks, which likely contributed to their frequent preservation in amber. The ongoing discoveries of new fossil taxa suggests that the diversity of Bruchomyiinae during the Cretaceous was likely much greater than it is today (Skibińska et al., 2019, 2023).