Question
does scale on my mistletoe die in cold=45F-or will it infest plants in my home

Answer
Dear Richard, I was surprised by the irony of your question, because I wasn't aware that mistletoe had any pests.  However, that is indeed the case and there are a few varieties of scale that will attack mature mistletoe.  Scale is a hard bodied insect and it is not affected by cold because of its protective covering.  Once it is inside it is possible to spread to your other plants.  Not extremely likely, but possible.  I would look for uninfested mistletoe, or try to clean off the mistletoe you do have.  Be careful to avoid the milky sap as it can be irritating.  There is one other thing that you could try to make it safe to bring inside.  Since I'm sure you're just using it for Christmas decoration, why not get some spray shellac, flat for more natural looking, glossy for more shiny, and spray seal it shut.  That would work for your purposes and dry in an hour.  Merry Christmas, Melissa