Bugs one appearing in dodgy cabaret (8)
I believe the answer is:
bacteria
'bugs' is the definition.
(I've seen this before)
'one appearing in dodgy cabaret' is the wordplay.
'one' becomes 'i' (Roman numeral).
'appearing in' is an insertion indicator.
'dodgy' indicates anagramming the letters (a dodgy or wrong order of the letters).
'cabaret' with letters rearranged gives 'bactera'.
'i' going inside 'bactera' is 'BACTERIA'.
(Other definitions for bacteria that I've seen before include "Cabaret I perform badly for the tiny organisms" , "Microscopic organisms, may carry diseases" , "Causes of many diseases" , "Agents of infection" , "Possible cause of disease" .)