Insect burrowing into unvariegated banana (8)
I believe the answer is:
Here is my best explanation:
'banana' is the definition.
(plantain is a kind of banana)
'insect burrowing into unvariegated' is the subsidiary indication.
'insect' becomes 'ant' (ant is a kind of insect).
'burrowing into' indicates putting letters inside.
'unvariegated' becomes 'plain'.
'ant' put within 'plain' is 'plantain'.
(Other definitions for plantain that I've seen before include "Low-growing plant; type of banana", "Tropical food", "Coarse banana", "Banana for cooking", "Cooking banana", "Shrub; green banana", "Weed", "Type of banana", "Banana-like fruit" and "Large banana - weed".)