In response to MO's interesting report, dessication certainly seems to be a problem with iris larvae during certain winters, certainly in captivity, and it would appear in the wild also. I imagine that the problem is complex; could this possibly linked to the significant desiccating effects of repeated frosts as well as a other factors affecting microclimate? Conversely in mild damp winters mould is also a significant threat to the over wintering larvae, although this phenomena may be greatly exaggerated in captivity due to the limited air circulation in a netting sleeve.
Camilla also suffers significant losses due to apparent dessication (larvae shrivel and harden) during some winters, both in the wild and in captivity, almost always towards the end of the winter, approaching the time at which one would be expecting to see the larvae preparing to become active again. I wonder if the larval mortality rate in iris during this phase is the factor that has the most influence upon whether or not we have a 'great' iris year...
Matthew's study is certainly raising some interesting questions.