Randy it's noble for your boys to shoulder the blame but to me there has to be something different about that hive at that time. This is what is on Eastman's (Kodak) website:  http://www.eastman.com/Products/Pages/ProductHome.aspx?Product=71001210&list=products

Eastman™ n-Butyric Anhydride 
Applications/Uses 
Flavorings
Fragrance intermediate
Pesticides
 Knowing that it was a hot day, could it be that:
1: The oxygen level in that hive was already dangerously low then adding the fume board just pushed it beyond the limit killing the bees by affixation? (Not sure how long that would take)
2: A chemical reaction happened with other vapors (acid, alcohol, water, bases) in the hive producing a strong enough to kill (unknown) pesticide.
These may seem left field but it gives though that waiting a minute or two between the removing of the top cover and the placing of the fume board might be in order on a hot day.

Cheers
 
 

             ***********************************************
The BEE-L mailing list is powered by L-Soft's renowned
LISTSERV(R) list management software.  For more information, go to:
http://www.lsoft.com/LISTSERV-powered.html