Now I may have been married longer than you (coming up on 20 years), so maybe our relationship is in a different state. I would have no problem, and without being patronizing, asking my wife if she wanted to learn to dive remarking that she has a strong fear of insects and asking her how she thinks she might respond.
I wouldn't automatically assume that just because she is afraid of bugs that she will be afraid of diving. I know several divers that are afraid of bugs, mice, snakes....that love diving.
I agree with everyone else, to (1) have her try snorkeling, (2) sign her up with a good, patient instructor -- certainly not in a class with you. If she is interested in diving and needs a little more time getting the hang of things, switch to a semi- or fully-private class. The additional $$ will be worth the piece of mind to both of you.
As for my wife, she does NOT dive. She is one of those people who can't put her face underwater. However, she enjoys the beach/boat while me and my two boys dive, so we still get diving-related vacations.
Whatever you do, don't force her. I have seen too many girlfriends / wives be brow-beaten into taking a class, only to (1) hate it and (2) eventually quit [either before or after certification]
Otter