Insect bite's coming up (4)
I believe the answer is:
gnat
'insect' is the definition.
(gnat is a kind of insect)
'bite's coming up' is the wordplay.
'bite' becomes 'tang' (I've seen this before).
'coming up' is a reversal indicator.
'tang' backwards is 'GNAT'.
(Other definitions for gnat that I've seen before include "Small, swarming insect" , "Insect like small mosquito" , "Tiny biting insect" , "Tang of a biting fly" , "Small biting flying insect" .)