I'm now able to issue a provisional estimate of the 2011 iris egg lay in and around Savernake Forest, Wilts - and it's bad news: unless I discover a couple of serious hotspots it looks as though the 2011 egg lay is around half that of 2011, itself a poor lay.
Having sampled much of the forest, it looks as though I'll find about 30 eggs & larvae this year, compared t0 60 in 2010 and 141 in 2009 (an exceptionally good year). Today, I searched 10 good trees that produced nine ova / larvae in 2010 and 16 in 2011, and found four.
The situation may be better in Bucks, Herts, Northants and Oxon where for reasons unknown the butterfly seemed to be in better numbers this year, and should consequently have laid more eggs. But the egg lay may be even worse in Sussex.
At this range it seems highly unlikely that 2012 will be a good iris year, but I'm more than happy to be proved wrong...