Unwanted bugs sting initially (8)
I believe the answer is:
needless
'unwanted' is the definition.
(I've seen this before)
'bugs sting initially' is the wordplay.
'bugs' becomes 'needles' (to provoke or annoy someone).
'initially' indicates taking the first letters.
The first letter of 'sting' is 's'.
'needles'+'s'='NEEDLESS'
(Other definitions for needless that I've seen before include "Unwanted" , "Without reason" , "Excessive" , "Unneccessary and unwarranted" , "- - to say" .)