Xenopygus analis (Erichson). Distributed from southern Mexico all the way down to Argentina, also found in the Caribbean and introduced in Hawaii. By far the most frequently encountered and most frequently collected Xanthopygina.
As they say, I would be a millionaire if I had a penny for each specimen I had identified in collections
around the world. With so many populations around central and south America, this is a going to be a cool phylogeography project someday.