It's obvious insect has infested this tropical staple (8)
I believe the answer is:
plantain
'tropical staple' is the definition.
Although both the answer and definition are singular nouns, I don't see how they can define each other.
'it's obvious insect has infested' is the wordplay.
'it's obvious' becomes 'plain' (similar in meaning).
'insect has' becomes 'ant' (I can't explain this - if you can you should give a lot more credence to this answer).
'infested' indicates putting letters inside (some letters are infested with others).
'plain' enclosing 'ant' is 'PLANTAIN'.
'this' is the link.
Can you help me to learn more?
(Other definitions for plantain that I've seen before include "Banana-like fruit" , "Low-growing plant; type of banana" , "Tropical plant like a banana" , "Green-skinned banana" , "Cooking banana" .)