I think it's probably bass wood (seriously). The only dowels I could find with the right diameter was at the craft store, so whatever wood they use for craft wood (I'm assuming bass). At first I was all concerned that I needed a really solid, strong wood like oak or something, but it's not a problem. Balsa might be too light, but anything that's easy to work with but still has enough strength to hold the screws in the bait will work fine.
-Brian