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For what it's worth (four years after the matter!), I'm pretty sure this is actually Stichopogon trifasciatus instead. S. argenteum has the abdomen all light grey, while S. trifasciatus has first tergite grey, next two black, next one grey, next three black, genitalia grey, and its grey is more of the steel-grey variety (like here). You can just make out that pattern through the wings.
For comparison, look at this guy:
http://bugguide.net/node/view/579680/bgimage