Insect collections retained in case of trouble (6)
I believe the answer is:
tsetse
'insect' is the definition.
(tsetse is a kind of insect)
'collections retained in case of trouble' is the wordplay.
'collections' becomes 'sets' (set is a kind of collection).
'retained in' means one lot of letters goes inside another.
'case of' means to remove the middle letters (outsides of).
'trouble' with its middle removed is 'te'.
'sets' put inside 'te' is 'TSETSE'.
(Other definitions for tsetse that I've seen before include "flies" , "African transmitter" , "source of sleeping sickness" , "carrier of disease" , "cause of sleepiness?" .)