Didymomyia tiliacea is a gall forming midge found on Lime.  The gall is a woody swelling, most often on upperside, conical above and hemispherical below.  In midsummer a inner gall sticks out from the cone, later falling and leaving a hole in the outer gall which then become covered over. 

Gall Adult

on Lime trees

Uncommon or under-recorded.

Unknown.