Insect's pungency brought up (4)
I believe the answer is:
gnat
'insect's' is the definition.
(gnat is a kind of insect)
'pungency brought up' is the wordplay.
'pungency' becomes 't'ang' (I've seen this in another clue).
'brought up' says the letters should be written in reverse (in a down clue, letters go up).
'tang' reversed gives 'GNAT'.
(Other definitions for gnat that I've seen before include "mozzie" , "Sucker (if female)" , "Two-winged fly" , "Tang of a biting fly" , "Insect like small mosquito" .)