Photomechanic can do this

I believe if the Title field is blank, Fotolia will use the Description field.

I believe if the Title field is blank, Fotolia will use the Description field.

Right, they do.
Since I discovered that, I use short script running ExifTool to just delete the titles before uploading to Fotolia (as I upload to each agency out of a specific folder, that does not affect uploads to other agencies).

Put the following line into a script / batch file (don't know how that works on Mac, on windows you can simply create file with the editor and give it the .bat extension, then run it with double clicking on it):

C:\Programs\ExifTool\exiftool.exe -L -k -overwrite_original "-IPTC:Headline=" *.jpg

where (obviously) the path in the beginning points to your installation of ExifTool.

This will delete the title in all jpg files in the current folder.

I believe if the Title field is blank, Fotolia will use the Description field.

Yes, but some sites ask for both, and I don't want to spend time to edit in different ways for different sites.

By the way I have noticed that Fotolia does not accept long titles, and generally my descriptions are much longer than the titles because I try to insert the more possible important keywords in it.

I think that Fotolia is a big "loser" from this point of view

You could just make them the same. AFAIK, DT is the only agency that won't accept a file if the two fields are the same. I just add one or two words to elaborate and make it different enough for them to accept.

e.g.
Title:
Woman wearing headset eating salad and smiling with thumbs up.
Description:
Beautiful woman wearing headset eating healthy salad and smiling with thumbs up.