Food that's green fed to insect (7)
I believe the answer is:
aliment
'food' is the definition.
(I know that aliment is a type of food)
'green fed to insect' is the wordplay.
'green' becomes 'lime' (lime is a shade of green).
'fed to' is an insertion indicator.
'insect' becomes 'ant' (ant is a kind of insect).
'lime' placed inside 'ant' is 'ALIMENT'.
'that's' acts as a link.
(Other definitions for aliment that I've seen before include "Nourishment" , "Something which nourishes - meal tin (anag)" , "Old word for food" , "Sustenance" .)