Insect collections kept in ether regularly (6)
I believe the answer is:
tsetse
'insect' is the definition.
(tsetse is a kind of insect)
'collections kept in ether regularly' is the wordplay.
'collections' becomes 'sets' (set is a kind of collection).
'kept in' means one lot of letters goes inside another.
'regularly' means one should take alternating letters (regularly take one letter, leave next etc.).
The alternate letters of 'ether' are 'te'.
'sets' put within 'te' is 'TSETSE'.
(Other definitions for tsetse that I've seen before include "cause of sleepiness?" , "flies" , "fly across Africa" , "Disease-carrying fly" , "source of sleeping sickness" .)