Insect breaking in to ferret's food store (6)
I believe the answer is:
pantry
'food store' is the definition.
(cupboard for storing food)
'insect breaking in to ferret's' is the wordplay.
'insect' becomes 'ant' (ant is a kind of insect).
'breaking in' indicates putting letters inside.
'to ferret' becomes 'pry' (both can mean to seek information).
'ant' put within 'pry' is 'PANTRY'.
(Other definitions for pantry that I've seen before include "Small room or cupboard for storing food" , "Room off the kitchen" , "Kitchen storeroom" , "Food store" , "Small storeroom for food etc" .)