I breed and grow my own silkworms. I have now bred several generations from the same original batch of eggs that I purchased. So far the silkworms seem to be healthy as all silkworms are, and I have not had any unusual die-offs. I am wondering if eventually, since I am really breeding siblings, I will eventually run into issues. Is the silkworm gene pool diverse enough to warrant for me to buy eggs from somewhere else and grow them and breed them with my current silks, or have they been domesticated for so long, that they are all essential related and have the same genes? In other words, there would be no benefit for me to seek out silkworm eggs from elsewhere.
I think with most invert colonies it's a good idea to get fresh stock after a time, I just don't know what that time is. The gene pool is only as big as the number of animals you had originally participating in it, not necessarily the length of domestication. However, I don't think they are as sensitive to inbreeding as vertebrates.
If the colony (is that a thing?) seams to be getting weak (high losses, sickly bugs, deformities, reduced reproduction rate) it might be a sign it's time to get some more bugs from another supplier for more genetic diversity.