True but not true. You do want to introduce strong genetics on occasion but you have to breed the worms to have strong genetics. And introducing new blood from a reputable source is extremely important. Silkworms have a terrible immune system and you will find that with new batches and old batches. The best thing is breeding your silkworms strong and true. However in the process you have to be prepared to lose hundreds of dollars in worms for good breeding stock. I have been working on my strong genes for 1+ years now.
And
@Tortdad why do you think the BSFL and Blue bottle flies died? Did they look dead or something?