>     in a cool, dry place and away from sunlight.  The active ingredient seems
>     particularly sensitive to UV.
 
I think I noticed this.  I hived a package of bees this spring, and
accidently I left the cage (with its Apistan strip) off to the side.
It sat right-side up in the sun.  When I found it a couple weeks later
the part of the strip stapled to the top of the cage was discolored and
darker, while the part hanging in the cage (mostly out of the sun) looked
normal still.
 
-Mike