Asimina species are generally regarded as the only host plant for the Zebra Swallowtail. For most of the East Coast, that means A. triloba which is a large tree. In Florida, we have many other Asimina species which are small shrubs. For more information on the butterfly, including a map of sightings check here:
http://www.butterfliesandmoths...
Also, butterfly bush is listed as invasive in Pennsylvania so I would not recommend planting it. Read here for more information:
http://www.birdsandblooms.com/...
