it is not that I have the solution approved yet, but my understanding up to now is the following: The butterfly viruses have two ways to spread: horizontally, i.e. between individuals in a livestock or vertically, i.e. from generation to generation. P. machaon caterpillars do not live in groups and therefore P. machaon specific viruses will have to spread vertically in nature to be successfully. On the other hand, if vertical transport has to be achieved, the individuals should not die, because the transportation from generation to generation would be stopped otherwise. So vertically spreading viruses have to be present at low levels in many individuals to survive. If now we enthusiastic butterfly breeders rear hundreds of caterpillars close to each other, horizontal transport happens additionally, which is not present in nature. Additionally, if raised in house, natural disinfection due to UV does not occur. Most of the UV does not pass glass, and if, it is the soft UV with little disinfection potential only. So we, or rather the butterflies, suffer from the disastrous illnesses.
From my experience with P. machaon spreading between cages does not occur heavily, but does, even if sanitation is followed. The problem is much worse if raised in house than outdoors. Additionally I noticed, especially the indoor/outdoor phase of the eggs is important, which leads again to the UV disinfection thesis.
In my opinion - no guarantee - discarding of the containers is not necessary. In my case disinfection was definitely successful. If you are not into the UV thing as I am, you can easily use conventional disinfection liquids. Good, but probably expensive are hand disinfection liquids, as used in hospitals. Eau de Javel (sodium hypochlorite) works very well, too. You can buy it as “bleach”. Some professional butterfly breeders use this for disinfection of monarch eggs….
I am not familiar with tropical Papilios. So I don’t know, if their caterpillars live alone or in groups and if all the above applies to them. Nevertheless I would be happy if my considerations are of any help.
Kind regards, Stefan