What is the title of this song on the Pupa OST?
Pupa's OST was composed by KONISHI Kayo and KONDO Yukio (who, together, make up the musical unit MOKA☆). Unfortunately, I think that's as good an answer as you're going to get, given that the soundtrack hasn't been (and, I'm guessing, never will be) released. 

If you liked the music in Pupa, perhaps you would like to listen to the soundtrack of Elfen Lied, which was also composed by Konishi and Kondo.