Ducks harbouring bug or parasite (6-2)
I believe the answer is:
hanger-on
'parasite' is the definition.
(thesaurus)
'ducks harbouring bug' is the wordplay.
'ducks' becomes 'hon' (I can't explain this - if you can you should give a lot more credence to this answer).
'harbouring' indicates putting letters inside.
'bug' becomes 'anger'.
'hon' placed around 'anger' is 'HANGER-ON'.
'or' acts as a link.
(Other definitions for hanger-on that I've seen before include "Someone who tags along" , "Persistent follower" , "A sycophant - he really clings" , "Dependent - sycophantic follower" , "Unwanted follower or dependant, parasite" .)