I have been trying to rear P. brassicae butterflies for some laboratory purposes. Using handpairing techniques I have managed to obtain already the second generation of larvae that are starting to pupate. Unfortunately the survival rate (for all the larval stages) is not great and some of the crysalides are starting to turn bright red before dying shortly after formation. Could this be some kind of virus or something? Or there could be some other factors impacting it? For example I have been experimenting with different foodsources and found out that the larvae fed with inner cabbage head leaves (white ones) are turning yellowish and getting more apatic until they die (but this was explained with the chemical changes within the cabbage as it varies by the leaf layers). All the food i have been given to them have been either grown personally or from known people therefore definitely free of any pesticides or insecticides.
As the butterflies are adapting from wild, could it be that the biological clock is playing some tricks and they are dying because in nature they should not be active anymore?
I would be happy for any suggestions for directions to look or find information or course of action.