Dung-fly regularly avoided one fruit (4)
I believe the answer is:
ugli
'fruit' is the definition.
(I know that Ugli is a fruit)
'dung-fly regularly avoided one' is the wordplay.
'regularly avoided' indicates alternate letters (letters removed at regular intervals).
'one' becomes 'i' (Roman numeral).
'dung'+'fly'='dungfly'
The alternating letters of 'dungfly' are 'ugl'.
'ugl'+'i'='UGLI'
(Other definitions for ugli that I've seen before include "West Indian citrus fruit" , "(Repulsive-looking?) fruit" , "Hybrid fruit, sounds nasty" , "so to speak, for > fruit" , "Mottled tangelo hybrid" .)