Bug a non-medical doctor to catch one (5)

I believe the answer is:

aphid

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'bug' is the definition.
(type of insect)

'a non-medical doctor to catch one' is the wordplay.
'non medical doctor' becomes 'phd' (I can't explain this - if you can you should believe this answer much more).
'to catch' is an insertion indicator.
'one' becomes 'i' (Roman numeral).
'phd' enclosing 'i' is 'phid'.
'a'+'phid'='APHID'

Can you help me to learn more?

(Other definitions for aphid that I've seen before include "Blackfly or greenfly" , "Small plant-sucking insect" , "little sucker" , "Small insect like greenfly" , "Fly" .)

I've seen this clue in the Sydney Morning Herald.

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