Fly northward from West Estonia (6)
I believe the answer is:
tsetse
'fly' is the definition.
(tsetse is a kind of fly)
'northward from west estonia' is the wordplay.
'northward' says the letters should be written in reverse (in down clue going up).
'from' indicates a hidden word.
'estest' is hidden in the letters of 'west estonia'.
'estest' backwards is 'TSETSE'.
(Other definitions for tsetse that I've seen before include "Disease-carrying fly" , "Bloodsucking African fly" , "carrier of disease" , "African transmitter" , "flies" .)