I'd never trust the pressure treated wood on the top. Consider using something else up top with the treated stuff forming the legs and support. If there's a chance someone will sit on the seat in a wet bathing (or birthday) suit, a chemical leach might at least become irritating. It's a picnic table, people use them that way. The problem with insects is usually at the point of wood contact with the ground so the treated stuff doesn't have to include the top. If I thought a table was treated on top, I would find another table. Just sayin'.
The more I do, the less I accomplish.