Insect back for bite (4)
I believe the answer is:
tang
'bite' is the definition.
(thesaurus)
'insect back' is the wordplay.
'insect' becomes 'gnat' (gnat is a kind of insect).
'back' says the letters should be written in reverse.
'gnat' back-to-front is 'TANG'.
'for' acts as a link.
(Other definitions for tang that I've seen before include "Strong flavour/smell" , "Sharp smell of gnat" , "Aroma" , "Strong taste; Chinese dynasty" , "Bitter aftertaste - prong" .)