I have been exclusively using virgin queens in my operation, since started producing them years ago. I liked using virgins as opposed to cells as I can cull optimimally. Often you will find candled cells where the pupae died, or the queen has deformities. (underdeveloped wings, one leg not working, etc) Allowing them to emerge in the incubator allows me to keep inferior queens from taking up a mating nuc,or even a full sized colony. Many people have had frustrations with introducing virgin queens. Sometimes its effortless, and sometimes they are rejected to a high degree. I've experienced high percentage takes, and very poor. I often noticed when holding queens in their nucs for instrumental insemination, that the queens appeared to be accepted and were fed in their cages. After the procedure, they were killed by the bees when released. This was puzzling to me. I then realized that the colonies that were killing their queens were constructing queen cells while the queen was caged, and those colonies were the ones that were rejecting virgin queens to a high degree. I started to wisen up. (It took a while) I would make the nucs up a week in advance of adding virgin queens, feed them syrup and let them sit after moving to another apiary. I have queens emerging weekly during queen season, so it was easy to plan. I would inspect the nucs after sitting 7-8 days and carefully remove all emergency queen cells from the brood frames, then add candy caged virgins. The nucs were then in a "hopelessly queenless state." They had no eggs or young larvae with which to make their own queen. Another alternative is to keep the virgin queen caged for the remainder of the 7 day period after the nucleus was made up. After the nuc aged seven days, remove queen cells before allowing access to the candy for a delayed release. This is my second choice as they would seem to let a few here and there die in the cage, and I would have to add another queen when i came to remove cells. After adopting this new procedure I noticed my take was consistently much more successful.