Both STLC and Bug Life Cycle are different.

STLC consists of 6 stages. they are

1)Test Initiation
2)Test Plan.
3)Test Design.
4)Test Execution.
5)Test Execution. 
6)Test Closure.

Where as bug life cycle starts with finding the defect for 
the first time and ends at the time it is fixed,In between 
it is assigned to varius status such as 
new,open,reopen,fixed,closed,defered,pending, rejected 
etc....