Insect runs around top of orange plants (9)
I believe the answer is:
beetroots
'plants' is the definition.
(beetroot is a kind of plant)
'insect runs around top of orange' is the wordplay.
'insect' becomes 'bee' (bee is a kind of insect).
'runs' becomes 'trots' (trot is a kind of run**).
'around' means one lot of letters goes inside another.
'top of' says to take the initial letters.
The first letter of 'orange' is 'o'.
'trots' placed around 'o' is 'troots'.
'bee'+'troots'='BEETROOTS'
(Other definitions for beetroots that I've seen before include "vegetables" , "plants" .)