Entomological specimen at university in Pennsylvania (4)
I believe the answer is:
pupa
'entomological specimen' is the definition.
(entomology is the study of insects)
'at university in pennsylvania' is the wordplay.
'at university' becomes 'up'.
'in' means one lot of letters goes inside another.
'pennsylvania' becomes 'pa'.
'up' inserted into 'pa' is 'PUPA'.
(Other definitions for pupa that I've seen before include "A chrysalis as of butterfly" , "So peacock may have appeared" , "middle stage" , "not yet adult" , "appearance of immaturity" .)