Bug has upsetting tang (4)
I believe the answer is:
gnat
'bug' is the definition.
(I know that gnat is a type of dipteran)
'upsetting tang' is the wordplay.
'upsetting' shows that the letters should be reversed in order.
'tang' back-to-front is 'GNAT'.
'has' is the link.
(Other definitions for gnat that I've seen before include "Small biting flying insect" , "Small (swarming) fly" , "a little bit of a nuisance" , "Stinging insect" , "Tang (anag.)" .)