Covered in aphides! (3)
I believe the answer is:
hid
'covered' is the definition.
(I've seen this in another clue)
'in aphides' is the wordplay.
'in' indicates the answer is hidden within the clue.
'HID' can be found hidden inside 'aphides'.
(Other definitions for hid that I've seen before include "Concealed in orchids" , "Stayed out of sight" , "Concealed from sight" , "Kept out of sight" , "wanted to be sought?" .)