Until they get this fixed (assuming they are working on that--I hope), you can still access the correct list by simply adding a parameter onto the end of the URL. If you add "&project=[state or province]ants", you should get the list for that particular state or province (assuming they have that data). Make sure to type the actual state or province name and not "[state or province]".
Here is an example, since examples are usually the easiest way to explain something. Below is the broken URL, and its corrected URL below that.
https://www.antweb.org/taxonomicPage.do?rank=genus&adm1Name=California&images=true https://www.antweb.org/taxonomicPage.do?rank=genus&adm1Name=California&images=true&project=californiaants
Edit: Updated the information a bit.
Edit: It appears they fixed the problem for the United States
Edited by dspdrew, May 10 2016 - 8:44 AM.