The pandilla pune±a is an example of collaboration between "Pachamama" and "Orthodox Celts". This is the group from Belgrade that performs celtic music, mostly irish an scottish folk. Three years ago we had a common concert in Novi Sad divided in three parts. We had to play one part, they had another by themselves and at the end we had to play something together. We have chosen three pieces from Peru and Ecuador and three pieces from Ireland. The examples from this concert are "pandilla pune±a"and "my litlle boat" (originally for celtic harp, but here the main melody is played on charango).
So I have to disapoint David. The violin heard in pandilla is played by "Orthodox Celts" member. She (Ana Djokic) terminated her studies of violin in the Academy of Novi Sad but uses a lot of 'catching by ear' system. That's exactly how she picked the pandilla main line.
In both groups 'picking by ear' is quite a common thing. Of course it's much better if you have written music. The problem is that usually you don't have. So you have to pick by ear the main melody, harmonization and then 2nd , 3rd voice etc. We usually put all that in some sort of very simplified notation, just to be on the safe side of not forgetting it.
I personally like very much violin incorporated in peruvian and ecuadorian folk. There is a very nice CD with a lot of harp and violin - music from Ayacucho (Ayllu Sulca is called, Ronald Wright collection.). I am pretty shure it is available in the States.