Etymology of Greek Word Muia??

From: Tom Lawrance (no email)
Date: 03/13/05 

Date: Sat, 12 Mar 2005 17:27:55 -0800

The PIE root section in the back of my American Heritage Dictionary
attributes a host of IE words for flies to a root mu-. However,
instead of attributing Greek "muia" and "mua" directly to *mu-, as the
words suggest, it attributes them to a suffixed form of *mu-, *mus-ya.
Can anybody tell me the reason for this?

Thanks very much in advance.