You're right that they will move onto something else. We only use bluegum here because it is so easily available but in Europe they use all sorts of trees and bushes, including fruit trees, bramble etc. It wouldn't take long for these stick insects to find some rare indigenous plant to munch on. But cutting down large swathes of bluegum to feed them on in captivity - now that sounds like a good, ecologically friendly thing to do.
I cut most of my food along Main Road near Lonehill. I can safely leave my car as I wander, cutters in hand, as there are always policemen (or women) carefully secreted behind the trees with speed cameras nabbing motorists along Main Road.
If you want more info on stick insects, there are some care sheets on our web site:
http://www.sa-chameleons.com. If all goes well, we hope to have some different species on display at the upcoming Reptile Show.