Adults also migrate during outbreaks. There has also been a more recent outbreak that peaked in 2004. You can now find them only with great effort, except for several small outbreak populations in Utah. We are working on ways to identify the centers from which outbreaks occur.
Many of these locations are certainly wrong. There is no way that Anabrus have been found in the Southeast or on Hudson's Bay. See maps on the singing insects website http://entomology.ifas.ufl.edu/walker/buzz/index.htm for a better range map or email me.