[UrbanK]

Does anyone happen to know if this is part of a larger work? I have looked at likely candidates on IMSLP but haven't been able to locate it.

 

[RobertJTh]

It's the middle movement from a violin concerto in B flat major. There are several performances at youtube, but I can't find the original score.
As often with works "by Pergolesi", it's possibly spurious.

 

[UrbanK]

Thank you! How did you find it if I may ask?

 

[RobertJTh]

When I couldn't find it at IMSLP at first, I thought it could be a movement from one of those Concerti Armonici that long were attributed to Pergolesi (Stravinsky even used themes in "Pulcinella") but now are proven to be composed by Unico Wilhelm Wassenaer. And the 2nd concerto indeed has a siciliano movement, but it's not the same.
Then I just googled a bit and came up with this:

https://www.muziekweb.nl/Link/U00001510171/CLASSICAL/Concert-voor-viool-en-strijkorkest-in-Bes-gr-t-Siciliano