For the last 8 years I've monitored Purple Hairstreak eggs along a section of drooping oak boughs on the south-facing edge of Flisteridge Wood, an ancient woodland site on the Oxford Clay in N Wilts. Counts have taken place in Dec / Jan. Habitat conditions have remained stable, with an abundant supply of large thick bud clusters. Here's the data -
2005 26 eggs in 1 hr 50 (too quick, = ~36)
2006 44 3 hrs
2007 30 3 hrs
2008 42 3 hrs 5 mins
2009 79 3 hrs 5 mins
2010 39 3 hrs 30 mins
2011 38 3 hrs 25 mins
2012 0 3 hrs 5 mins
Clearly, something has gone seriously wrong with Brother Quercus here this year. I'd anticipated 30-35 eggs, largely on account of the good week we had in late July. I can only put this collapse down to the impact of the bad early July on the adults.
I did something similar in Hartley Wood, near Selborne in Hampshire, during the mid 70s to late 80s, but never drew a blank, though numbers fell from a massive 226 in 1976 to 12 in 1977.
Message, don't expect to see hoards of Purple Hairstreaks next year... The legacy of 2012 is dawning...