Destructive insect (6)
I believe the answer is:
'destructive insect' is the definition.
(I've seen this before)
This is all the clue.
(Other definitions for locust that I've seen before include "It strips plants" , "plaguey type" , "Grasshopper of warm regions" , "Destructive insect; tree" , "Destructive migratory insect" .)