If no one with scientific experience chimes in:

1. your seedlings will be variable but largely a mix of the parents so you will have some level of borer resistance.

2. I also believe planting more birch nearby will provide a place for the borers to breed and endanger other trees the same borers like.

Example, my kid shares have my genetics. He goes to daycare and plays with the other little germies. Then he catches a cold and these germs grow stronger until POOF! He sticks his grubby mitts in my mouth and I catch a cold ready made for my genetic profile.

Like I said, not very scientific. Do the same borers affect all birch?

^ Yes, bronze birch borer.

I once had a single specimen of "Crimson Frost" birch. It was hammered hard by borers before I had the sense to check into its gradual demise. Not the same plant as yours, but.....

+oM

All birches are to varying degrees susceptible to borers. They are also not terribly long lived trees in general and shorter lived in warmer climates - in Z4 and colder they can reach great age and size. There are some systemic root drench insecticides - Bayer Advanced is one - which provide good protection from a number of pests, borers included.

At our old house there were several European White Birches on the street. They were nice big trees that made the neighborhood look better but after awhile every one of them was attacked by bronze birch borers. Now there isn't a single birch on that street. Where you are you may have better success but here I've seen 10 year olds get killed by the borers. So I'd personally avoid getting more birches and take really good care of the ones you have. On a side note, does anyone know if Youngii Birch are susceptible to the borers? I've always wondered about that.

Agree with Mainegrower. I know of places, including my own land, where regular paper birch achieves much greater size and longevity that most people would consider the norm. They are growing among northern white cedar (Thuja occidentalis) in cool, spring-fed swamps. They like it there!

Also right along Lake Michigan, again here in WI, are some rather impressive paper birch. It's always cool there on days when inland areas are quite hot.

+oM