Use up reserves of energy mating — stop! (both stripped) (3,4)
I believe the answer is:
eat into
'use up' is the definition.
(synonyms)
'reserves of energy mating stop both stripped' is the wordplay.
'reserves of energy mating' becomes 'eatin' (I can't explain this - if you can you should believe this answer much more).
'both stripped' indicates the central letters (outside letters of both words are removed).
The middle letters of 'stop' are 'to'.
'eatin'+'to'='EAT INTO'
Can you help me to learn more?
(Other definitions for eat into that I've seen before include "run down" , "Consume (resources)" , "Etch" , "start wearing out" , "Corrode (something)" .)