SNMP V3 Traps Question

Hi,
I have an agent device that will only be sending SNMP V3 traps to a management system.

When I define the trap destination for the management system on the agent, do I still need to define the user (security name) on the agent using the USM, or is that only necessary on the management system?

Does anything need to be defined in VACM?

Thanks for the help,

George