Harass insect (3)
I believe the answer is:
bug
I believe this is a double definition.
'harass' is the first definition.
(I know that bug is a more specific form of the action bedevil)
'insect' is the second definition.
(I know that insect can be written as bug)
(Other definitions for bug that I've seen before include "Hidden microphone" , "Listening device, insect or electronic fault" , "Secret listening device" , "Irritate" , "Harmful microorganism" .)