Getting a username auto populated based on two fields in the NEW DEFECT creation box

Hi All,

I have the following requirement to acheive and appreciate all your help.

We have two fields in the Defects module - Lets say Priority and Severity. Based on the value we select in these 2 fields, One username should autopopulate in the Assigned to (BG_RESPONSIBLE) field.

Eg:

Priority : 1-Major

Severity: 4-Low

Based on the above two values, the following field should autopopulate the below value

Eg:

Assigned to: king.r

I am able to achive this by putting the below  code, in "Bug Field change" Event.

Sub Bug_FieldChange(FieldName)
  On Error Resume Next
         if (Bug_Fields.Field("BG_SEVERITY").VALUE = "4-Low" and Bug_Fields.Field("BG_PRIORITY").VALUE = "1-High") then
            Bug_Fields.Field("BG_RESPONSIBLE").VALUE = "king.r"
           end if
  On Error GoTo 0
End Sub

However, i want this condition to be met only in the NEW DEFECT Creation window(either from Defects module or Test Lab Manual Runner or Test Plan -Linked defect tab) and not in the Details page once created or when we are updating the defect at any later time. whatever value is there at that time, it should be there as it is when updating the defect.

Thanks