Wasp he researched gathers in fields (7)
I believe the answer is:
spheres
'fields' is the definition.
(sphere can mean an area of expertise or field)
'wasp he researched gathers in' is the wordplay.
'in' indicates a hidden word.
'SPHERES' is hidden within 'wasp he researched gathers'.
(Other definitions for spheres that I've seen before include "balls" , "Areas" , "Globes" .)