Ask Mr. Smarty Plants

First of all, Erythrina herbacea (coralbean) usually dies to the ground in Austin in the winter and regrows with great vigor from the roots in the spring.  In fact, I checked my plant yesterday and found new growth beginning around the old dead stems.  The termites you found in the stem of your plant were no doubt feeding on the dead material (the cellulose, to be specific) that they found there.  This is what termites normally feed on—dead plant material.  Here is a little more information about termites:

There are three types of termites that occur in Texas:  desert termites, drywood termites and the ones that, most likely, are the ones you found in your plant—subterranean termites. Additionally, there are two types of subterranean termites—native subterranean termites and Formosan subterranean termites.  The latter have been reported in Travis County and are considered to be more aggressive and destructive than the native species. The normal food for termites is dead and dying wood and in nature this is beneficial in that it keeps fallen trees and other woody wastes from accumulating; however, when the termites find their way into human structures they become an expensive pest.  I was surprised, however, to find that although generally all termites feed on dead cellulose, the subterranean ones have been known to feed on the dead heartwood of living trees and the Formosan subterranean termites have been known to feed on more than 47 living plant species including Morella cerifera (wax myrtle) and Prunus caroliniana (Carolina laurelcherry).  Desert termites also feed on living plant material, but they feed on primarily grasses of rangelands and eat surface material rather than tunnel into wood.  It is doubtful that your infestation was desert termites. I spoke with Elizabeth "Wizzie" Brown (512-854-9600), the Entomology Extension Program Specialist for the Austin area at the Travis County Texas AgriLife Extension office to find out how common it is for termites to feed on living plant material rather than the cellulose of dead material.  She said that she had seen whole trees hollowed by Formosan termites in Louisiana, but she was not aware of them attacking living plants in the Austin area.  I would guess that it is the dead cellulose material that even the Formosan termites (if those are the ones in your plants) are after rather than living plant tissue and I suspect that you have little to worry about with termites eating the roots of your plants.

Texas A&M AgriLife Extension offers information about different termite control methods in Commonly Asked Question About Termite Control. You can also read information about termite infestations and various treatment methods from Termites 101.org (sponsored by Orkin). These instructions are focused on controlling termites in human structures.   Again, I asked Wizzie Brown about treatments for termites on plants and she said that she didn't know of any specific treatment since this has not been a serious problem.  Even for the desert termites that do cause problems for ranchers, there are no pesticides labeled specifically for controlling them.

I don't want to be an alarmist, but there is a good chance that these same termites that you found in your coralbean could also have infested your house.  It might be a good idea to have it checked by a professional pest control company.