Relatives turn in insects (5)
I believe the answer is:
aunts
'relatives' is the definition.
(aunt is a kind of relative)
'turn in insects' is the wordplay.
'turn' becomes 'u' (a 'U-turn' is a kind of turn).
'in' is an insertion indicator.
'insects' becomes 'ants' (ant is a kind of insect).
'u' going inside 'ants' is 'AUNTS'.
(Other definitions for aunts that I've seen before include "Female relatives, usually older" , "relatively speaking" , "Relatives get an odd US tan" , "Sally and others" , "Relatives get a peculiar US tan" .)