Desert bug (6)
I believe the answer is:
defect
This clue is a double definition.
'desert' is the first definition.
(I know that desert can be written as defect)
'bug' is the second definition.
(I've seen this before)
(Other definitions for defect that I've seen before include "Abandon one's country in favour of an opposing one" , "'Flaw, imperfection (6)'" , "error" , "To change sides dishonourably" , "Want or imperfection" .)