Nosh for an insect larva (4)
I believe the answer is:
grub
This clue is a double definition.
'nosh' is the first definition.
(I've seen this before)
'for an insect larva' is the second definition.
(grub is a type of insect larva)
(Other definitions for grub that I've seen before include "Slangy food or kind of larva" , "Caterpillar - food" , "Worm-like larva of an insect" , "Food - worm" , "Food (informal)" .)