INSERT Query - Insert New Data Only

Table TBL_NEWDATA is used to append new data to table TBL_PERSON_ALLOCATIONS.

TBL_NEWDATA { Person_ID, Department_ID }
TBL_PERSON_ALLOCATIONS { Person_ID, Department_ID, ... }

I need to devise a query to append data for a particular Department_ID from TBL_NEWDATA to TBL_PERSON_ALLOCATIONS where that data does not already exist there. i.e. for Department_ID 'Research', I would want to append 'Person_ID', 'Department_ID' (in this case: 'Research') to TBL_PERSON_ALLOCATIONS for any tuples not already held.

INSERT INTO TBL_PERSON_ALLOCATIONS (Person_ID, Department_ID)
SELECT Person_ID, Department_ID
FROM TBL_NEWDATA
WHERE TBL_NEWDATA.Department_ID='Form...'

[code]...

This Query takes a single argument from a control (Forms!Main!IN_Department), and this is the Department_ID to be updated.Is there any way to do this using a single query or will I have to use sub queries? I'd hoped not to as to keep the database as concise as possible.