Disorientated leaf insect (4)
I believe the answer is:
flea
'insect' is the definition.
(I know that flea is a type of insect)
'disorientated leaf' is the wordplay.
'disorientated' is an anagram indicator.
'leaf' with letters rearranged gives 'FLEA'.
(Other definitions for flea that I've seen before include "source of infestation" , "Little jumping insect" , "In one's ear, it's a stinging rebuke" , "Bug" , "In your ear, this insect is a rebuke" .)