Sweet smell associated with insect (6)
I believe the answer is:
humbug
'sweet' is the definition.
(boiled sweet)
'smell associated with insect' is the wordplay.
'smell' becomes 'hum' (I have seen 'Unpleasant smell ' mean 'hum' so perhaps 'smell' could also mean 'hum').
'associated with' means one lot of letters go next to another.
'insect' becomes 'bug' (bug is a kind of insect).
'hum'+'bug'='HUMBUG'
(Other definitions for humbug that I've seen before include "Peppermint confection" , "Trick; rubbish" , "Noise of a bee with an insect makes a sham" , "It's stuff and nonsense about the sweet" , "talk that's deceptive" .)