I take it that you are asking what humidity would be appropriate and if the ootheca will hatch if refrigerated?
I have had a terrible time hatching European oothecas myself so I really couldn't tell you the trick to it. Now when I find them in the area I live, if there is a high concentration of them, I put them on other similar environments that do not have any oothecas. It seems that if they are allowed to warm up for more than a couple of days that they should not be refrigerated again. I have a feeling (those of you who have had success with Europeans can correct me if I am wrong) that after their cooling period that any kind of consistent heat source, even room temperature, will cause the eggs inside the ootheca to start developing. I have tried different scenarios in hatching my European ooths in the past but in the end I just keep European oothecas outside and let them hatch naturally.
