Checked all wild larvae today. All present and correct, and healthy. So none of them desiccated during the ten day spell of bitter north to easterly winds (though none was in a place significantly exposed to those winds).
Having followed larvae through in the wild for four winters, it appears that 'desiccation' is more of an issue in captive breeding than in the wild. I have recorded one 'desiccated' wild larvae in four winters, out of >100. One thing I can say quite categorically is that iris larvae behave very differently in the wild to how they behave in captivity. They are almost different animals.
Other good news is that, with a few days to go before larvae come out of hibernation, this winter's loss to (assumed) tit predation is under 20%, compared to >60% in the first two winters (varying sample size though).