I use B.t., and I apply it when I see the caterpillars on the leaves. No point spraying beforehand, IMHO.

Last year's chomping would probably not have directly affected this years buds, since, as far as I know, the flower buds are set after the caterpillars have finished. However, less vigor caused by leaf loss could indirectly lead to lower flower production, in the same way lack of sunlight would.

Don't panic, these pests take weeks to do significant damage to otherwise healthy trees. Remember that your trees can easily tolerate some damage, you just need to prevent heavy defoliation. You have plenty of time for this!

Although the linked article from 2008 is looking at just one region of New England I think it raises an important point that there are more than one catepillar/moth at work in terms of tree devestation. Yes the winter moth continues to be the biggest bully on the block but the gypsy moth, fall canker worm, the forest and eastern tent caterpillar and the spring canker worm, are doing a good bit of damage as well.
According to the article it took the introduced parasitic fly about ten years to knock down the population in Nova Scotia I believe this would be year six for Ma.
I have chosen not to spray as the damage/stress to my oaks has not been significant.

Here is a link that might be useful: Caterpillars

Also see the UMass Extension Landscape Message posted above for more information on treatment.

Claire