The wax moths are a small group of micro moths, which are all on this page:
http://www.lepiforum.de/lepiwiki.pl?Fotouebersicht_Galleriinae. *
Sorry for the German, but there is no English version of this site.
There was another post in this forum, where somebody wondered about hundreds of caterpillars in his cellar, coming from behind styrofoam plates:
http://www.lepiforum.de/1_forum.pl?page=1;md=read;id=64173
Therefore it is quite clear, that they can use it as their only food source!
Wax moth larvae are also frequently bred as feed for geckos or as fishing bait for anglers. On some of these web pages was mentioned, that the larvae can escape from plastic boxes by biting holes in smooth or thin plastic. While some other caterpillars are able to do that too, these ones obviously can also digest it. That means they must have enzymes or microorganisms in their digestive tract, which can decompose plastic.
With some thoughts about, what wax is, this also makes sense: Waxes are lipids with long chains of hydrocarbon (
http://lipidlibrary.aocs.org/Lipids/waxes/index.htm). To be able to digest bees wax, the caterpillars must break these chains into pieces.
And this is, how styrofoam looks:
http://en.wikipedia.org/wiki/Polystyrene_formation.png - same hydrocarbon chain, with bulky phenyl rings on every second
carbon atom. Other forms of plastic, like polyethylene or polypropylene are much more similar to the chains in bees wax. I guess, all of these types of plastic could be used as food source for the caterpillars, when one presents it to them in an edible form, like the yummy styrofoam...
* Basically three species behave similar, Aphomia sociella (the bee moth), Galleria mellonella (the greater wax moth) and Achroia grisella (the lesser wax moth), probably they are often referred to together as bee moths.