Any thoughts, @chrisvanswaay? Just trying to get a consensus here before merging one into the other.

http://lepiforum.de/lepiwiki.pl?Cupido_decolorata
https://fauna-eu.org/cdm_dataportal/taxon/c24b18f7-5ac6-4628-8cb1-cd09e4cbb2bf

Some remarks. "Decolorata" was used in the original description. In the European checklist by Wiemers et al. "Cupido decoloratus" is used, which is grammatically correct. Generally, in that paper generic and specific names were placed in gender agreement, as is required by the Code. However, there is a tradition in the majority (but probably not the whole of) lepidopterological community to use the original spelling of species names, NOT following gender agreement (against the Code!). Recently, a paper objecting the decision made by Wiemers et al. appeared, see https://nl.pensoft.net/article/34187/
This paper strongly recommends to use "Cupido decolorata".

Thus the situation became more complicated... :) However, the situation here, having the same entity splitted under two names, is stupid and inconvenient (say, if one wants to see all observations on the same map, or whatever). I strongly recommend to resolve it somehow, in one way or another. I cannot recommend the "preferred" name, but I think in a sense it does not matter; after stabilization it would be possible to change the gender to the concensus version, if necessary. If it is hard to choose, we can at least toss a coin. :)

@jakob @chrisvanswaay What do you think?

This is a purely taxonomic issue. I am not a taxonomist, but I would be completely OK with your proposition (to base on Wiemers et al except that 14 species). It would be grate to have a consultation of an experienced taxonomist, but I am afraid we do not have many here... Among knoledgeable people we do have, some might not be interested in this problem (for whatever reason). But let us try. I will also tag some people from North America, hoping they may give a good advice.

@chrisvanswaay @ronan_a @yoshik @rafaelmatias @mnauky @jkt @okoem @cossus @nlblock @rosslayberry Could you please read the above discussion and say a few words on your opinion? Also, if you want to ask others, do not hesitate to tag them here. Thanks.

A link to the Wiemers paper: https://zookeys.pensoft.net/article/28712/. I think the authors list contains most of the taxonomists on butterflies in Europe, the paper by Erik van Nieukerken the other few.
For some reason taxonomists always fight with each other.

Take my opinion for what is worth, as I'm not a Taxonomist (nor a professional Lepidopterologist, despite my love and 'afficcion' for the area), my main research area has been seabird ecology.
Regarding the above issue, I'd just follow the CODE, as that seems to be the only (in my opinion) objective and sensible thing to do, being this apparently simply a gender agreement issue (Arts. 31.2 and 34.2 of the code); Cupido is a masculin noun, thus it should be C. decoloratus; this could be applied to other taxa in this website, namely Carcharodus tripolinus (which is currently included as C. tripolina).

I'll transcribe below art. 34.2:
"Article 34. Mandatory changes in spelling consequent upon changes in rank or combination
34.2. Species-group names
The ending of a Latin or latinized adjectival or participial species-group name must agree in gender with the generic name with which it is at any time combined [Art. 31.2]; if the gender ending is incorrect it must be changed accordingly (the author and date of the name remain unchanged [Art. 50.3.2])."

Cheers

My experience is almost entirely limited to African Lepidoptera, but yes, we ignore gender agreement and use the spelling employed in the original description, all while being aware that it doesn't follow "the code".

At this point in history, I think this is of good practical use. Genera are constantly being revised, so there's not much stability. Take Brakefieldia, for example, which includes a number of species that, in the past 30 years, have been placed in combination with 4 or 5 different genera. Until things settle down, have the specific name change spelling would lead to confusion.

In regards to iNaturalist, I'd suggest we follow suit with what is in actual practice. Keeping to species with which I have familiarity, yes, Bicyclus dentatus may be correct according to the code, but those who have anything to do with African Lepidoptera will see that and wonder about the choice of spelling and likely seek to correct it. In that case, following the code is actually going against the grain, and introducing more confusion. The majority of Lepidopterists may be "rebelling" on this point, but most of us are in agreement that breaking the rule makes good sense, so we've made a rule unto ourselves.

Someone has already linked this article above, but it's more articulate than I and deserves attention: https://nl.pensoft.net/article/34187/

Someone also mentioned making sure that, with whichever spelling is chosen, the other one remains as a synonym. I think this makes good practical sense (though I believe it should happen automatically).

Lastly, should the decision be to go with decoloratus, don't be surprised when someone(s) neck deep in butterflies flags it to say it's spelled wrong.

Sorry! Last post for now.

Let me quote Adam Cotton, who is a world expert on Papilionidae and is based in Thailand, and is generally a stickler for "proper" nomenclature:

"There is a general agreement among lepidopterists that gender agreement articles (31.3 & 34.2) of the ICZN Code should be ignored and original spellings be used except where mandated by other articles of the Code, as per the resolution of the Societas Europaea Lepidopterologica discussed by Sommerer (2002) (To agree or not to agree - the question of gender agreement in the International Code of Zoological Nomenclature. Nota Lepidopterologica 25: 191-204, available here: www.biodiversitylibrary.org/page/41371975 ).

Eminent lepidopterists around the world follow this recommendation, including the ICZN Commissioner who is an expert on nomenclature of Lepidoptera, Gerardo Lamas. Here's an example of a recent paper which mentions this issue:
Kitching, I., Rougerie, R., Zwick, A., Hamilton, C., St Laurent, R., Naumann, S., Ballesteros Mejia, L. & Kawahara, A., 2018. A global checklist of the Bombycoidea (Insecta: Lepidoptera). Biodiversity Data Journal 6: e22236. doi.org/10.3897/BDJ.6.e22236

The major exception is the Japanese Lepidoptera community who still conform to gender agreement articles."

To be blunt, from an iNaturalist perspective, I think this disagreement means basically nothing. If one name is merged into another, the "old" name is still retained as a synonym attached to the remaining one. Thus, a search for either spelling will still lead to the correct taxon and the data of interest.

Both sides make a good argument. We should just flip a coin and pick one to merge into the other on iNat. Meanwhile, the taxonomic disagreement can continue to play out in the literature. :-) People will still be able to find sightings data on the species here, regardless.

(And I don't say any of this to be dismissive of the debate itself. I love taxonomy, discussions of species limits and naming, etc. In this minor case, I just don't think it's particularly relevant to iNat.)

I've made the relevant changes. Let me know if something is missing.