Spruce Bark Beetle Infestation

[Harry J. Donahue]

I am located in South Central Alaska near Anchorage.  Over the past few 
years, I have lost over 50 of my largest spruce trees.  I have been 
spraying with Sevin(Carbaryl) up to 20 feet.  Is there a life cycle for 
these insects, or am I forced to spray on an annual basis forever???Any 
suggestions would be very much appreciated.
Harry Donahue  E Mail HJD at aonline.com