pupal behaviour

[Felix A Vergara MD]

I am a high school senior.  In biology II  we have a project.  We are raising
drosophilas to study the genetic variations.  All what happened in my flask was
pretty normal ( similar to my classmates ).  But now most of my pupas stayed on top
of the food.  My colleagues' pupas are up the walls.  I am worried because I suspect
that my experiment is going wrong.  Any body have seen this behaviour before?  Are
my pupas dead? I will appreciate your answers and advices.  Thank you. Joe.