I can double check the dose for you, what is your dragon's weight?
I couldn't tell by looking, but what is the strength of the Strongid, does it specify?
Hookworms definitely should be treated, because they can do damage to the intestinal
lining. I don't think that the dubias are the source of hookworms, so definitely hold onto
your colony for him.
As AHBD said, they do have a normal gut flora of bacteria which usually doesn't affect
them, unless it gets out of balance.