I used to visit Fauna Europaea as a reference of updated scientific animal names, but it seems is now out-of-date. Alternatively I seek in the search option of GBIF.org, and usually it works, but sometimes you get surprises like:
Musca festiva as accepted name for Chrysotoxum festivum (synonym), written as: Musca festiva (=Chrysotoxum festivum) https://www.gbif.org/species/4516839
In general GBIF uses Catalogue of Life as their taxonomic backbone. It may be a case that CoL uses that treatment. That would be the first thing to check.
I do not know how often they sync to CoL.
Of course it is also possible that trying to maintain a universal taxonomy is an overwhelming task and they cant keep up.
Chrysotoxum festivum and Chrysotoxum arcuatum have been very problematic in the recent past. Their meaning being altered by designation of lectotypes: https://doi.org/10.1111/zoj.12052
and then reverted back to the previously widespread use by designation of neotypes as ruled by Opinion 1982 of ICZN: https://www.biodiversitylibrary.org/page/33818094#page/251/mode/1up
This perplexity seems to be ongoing.
Just like iNat, GBIF uses Catalogue of Life as its starting point in building its taxonomy. CoL itself uses other basic taxonomic providers like Systema Dipterorum: https://www.catalogueoflife.org/data/dataset/1101
Neither CoL, nor Systema Dipterorum list Chrysotoxum festivum at all (as valid or invalid) so it’s probably GBIF’s taxonomical decision. Unfortunately they don’t provide details for their decisions.
If you want to provide feedback, it’s probably best to contact the original taxonomic provider - Systema Dipterorum - and ask them to add the name: http://diptera.org/GetInvolved
This way it should reach everyone that comes next in the chain, including CoL and GBIF
iNat does not follow CoL. CoL is one of 2 external sources, along with Encyclopedia of Life that automated ‘easy’ import tools have been built for to get new names.
iNat tries to follow the authorities listed here. For groups where no authority is listed, there is no resource formally linked to. iNat taxonoimy authorities