What type of insulation should be used to deter subterranean termites?
I can verify boron treated EPS degrades over time. Boron is water soluble, so the treatment doesn't last through more than a couple wet seasons.  



There's apparently a new insecticidal treatment being sold under the trademark Preventol.  It's unclear how many years this treatment will remain effective. In any case, I think soil treatment should be used whenever EPS is installed below grade to help long-term repel insects. 

The foamglas product looks interesting. It's made of silicon instead of polymer. It would still be nice to see a long-term test, though. Until someone buries it for a few years, the claims of the manufacturer can't be verified.