Out of the gall and into the jar

When I opened the thistle gall, I exposed four Canada thistle stem gall fly (Urophora cardui) larvae. These flies can reduce the seed production, and thus the spread, of the invasive Canada thistle (Cirsium arvense).  Therefore, I decided to give the larvae a new home to replace their broken gall.  I put them into a jar, but had trouble deciding where to keep the jar.  I worried that the jar might not provide as much insulation as the gall, and thus that the larvae might freeze if kept outside.  However, inside the house it was warm; would the larvae take this as a cue that spring had arrived and pupate several months early? 

A larva (left) and three pupae (right) of the Canada thistle stem gall fly (Urophora cardui).

Five days later, three out of four of the larvae have pupated.  Perhaps their pupation was just triggered by the destruction of the gall, but I think it is likely that the warm temperature inside the house played an important role.  The next stop for the jar is the garage, where I hope the cooler temperature will halt their development until a more appropriate time.