Lythria (Lythria) plumularia (Freyer, 1831)

Pl. 2: 5a–5h

Fidonia (Orig. “Gen. XCVIII. Fidonia. Geom.[etra]”) plumularia Freyer, 1831: 68, Tab. 36, fig. 3. TL: [Switzerland]: Thur (ST) Distribution. Alps in south-eastern France, northern Italy, southern Switzerland, through Austria to southern Germany (Bavarian Alps).

The placement of the genus Lythria in the Geometridae system remained controversial until the end of the first decade of the XXI century. Only molecular genetic studies, which included, in addition to the mitochondrial COI gene, 4 more nuclear markers, were able to link this genus convincingly with the Sterrhinae subfamily. An accurate tribal association was proposed only a few years ago (Sihvonen et al. 2020), and was also based on data of multigene analysis (11 molecular markers). The difficulty of using morphological characteristics of the genus Lythria for its tribal association was due to the fact that its widespread and well known members have “advanced” features, and some structures (e.g. the signum in the female genitalia) are secondarily lost. If the morphology of both male and female genitalia of L. (M.) venustata (a basal branch of the generic tree of Lythria) had been available to lepidopterists in the pre-molecular epoch, this species could well have been the key to understanding the place of this genus in the Sterrhinae system.

Now that the males and females of all recent Lythria species are known, it is possible to compile a complete identification keys to this genus. We provide two such keys below (one by external characteristics, and one based on the structure of the genitalia).