creating alias for table names in a an Append query

wanting to know how to create aliases for the two tables
1. NewTasksBeingAdded
2. [table Excel data]

for the follwing sql statement
From what I understand the where clause (re written from joins to the where ) will not execute without the tablenames being aliased

StrSQL = "INSERT INTO NewTasksBeingAdded ( [Activity ID], [WBS Code], [Activity Name], Area, Line) " _
& "SELECT [TASK Excel Data].[Activity ID], [TASK Excel Data].[WBS Code], [TASK Excel Data].[Activity Name], " _
& "[TASK Excel Data].Area, [TASK Excel Data].Line " _
& "FROM [TASK Excel Data], NewTasksBeingAdded " _
& "where [TASK Excel Data].[Activity ID] = TASK_BackUP.[Activity ID] " _
& "and TASK_BackUP.[Activity ID] Is Null"