Intriguingly the ancient people who set up trading posts in the Japanese islands to which the natives brought silkworm bolls (circa 100BC to 300BC) appear to have been the same people who are buried in their tartans along the Silk Road in West Central China.
So maybe the silkworm business went both ways up and down that road (as far as the technology was concerned), with local insects of various species doing the hardpart.
You do, of course, realize that whether the account of Justinian commissioning two Persian monks to smuggle silkworms back is mere legend and the European silkworms are different from the Chinese is quite irrelevant to my point: the Empire began an indigenous silk industry, c. 550, 1. During Justinian's reign, and 2. after the 'fateful' year 538, which industry grew and flourished, despite the hard times of the next century.
I think you already know what my 'take' is on that. I've been unable to make an air-tight connection though. Maybe if we found some mummified European silk-worm coccoons in Japan.
BTW, I just completed reading Stephen Oppenheimer's book, Out Of Eden, I was suprised when he stated that the oldest (undisputed) Mongoloid skeleton ever found is only 10k years old. I'm beginning to think that most of China was covered with the Jomon - Ainu type. James Chatters (of Kennewick Man fame) says that he thinks today's Asians and Europeans both split from this group. Oppenheimer explains the 'X' gene (European) found in only European and American Indians as having been from a 'branch' that was split by the Toba (super-volcano) explosion 74,000 years ago. Everyone in between was killed...breaking the link.