Kleidocerys resedae vs privignus
This comparison was created a while back for a Dutch forum and I just reworked it into a German version, so figured I might as well do an English one too :o)
The status(!) and identification of these two "species" is highly problematic. Also, it should be noted that these are the two "larger" Kleidocerys spp and that there is a comparable pale/dark duo of "smaller" Kleidocerys spp (K. ericae and trucatulus).
IF/WHEN (?!?) the two are seen as separate species, then K. resedae is considered to be the paler species, found mostly on Birch (but also on Alder!) and K. privignus is the darker species that develops on Alder. The discussion is highly complex and confusing, mostly because one of the leading publications on the subject (Carayon, 1989) is unclear/confusing in itself, as discussed here (in German):
The larger arrows point to the space between the second and third row of punctures on the clavus, that is supposed to be clearly contrasting dark in privignus, but on darker specimen of resedae the interpretation of this is highly influenced by viewing angle and lighting. To me the continuous streak of black on the hind margin of the corium is more helpful, but probably not 100% diagnostic either.