Its stupid (from a Todd POV) that the humans would wait until a meeting with him to deploy such a weapon - if it was their intent to betray him. 2 seconds of thought from Todd and surely he'd be thinking "they would complete fools to betray me now".
I think Todd was more worried about what would happen to the wraiths if they no longer needed to feed and took the opportunity to prevent that from happening.
Why wait until now?
He's been onboard with this plan since The Queen. Now he has doubts? Not buying it.
That as IMO the point of his conversation with Keller and I think he always had some doubts about the plan that's why he altered if somewhat in The Queen nad Teyla wasn't going to allow him to get away from the plan she made that pretty clear at the end of The Queen.