The giant Salmonflies of the Western mountains are legendary for their proclivity to elicit consistent dry-fly action and ferocious strikes.
Wax on, wax off... :)
We are slaves to our senses...:)
A while back, when I posted the above question, I also posed it to Gary Borger on his site. Apparently he'd responded:
http://www.garyborger.com/2010/01/07/caddis-pupa-husk/
Gary Borger says:
Hi Paul, No one that I know of in the scientific literature has seen caddis pupa pumped full of gasses. They have seen and clearly showed that there is molting fluid between the pupal husk and the enclosed adult and that it makes the pupa glisten.