The situation is even more tricksy than I suggested in my previous posting, for there appears to be less suitable foliage around this late summer / early autumn than during the previous two years, at least from ground level.
I've searched and graded (subjectively but hopefully consistently) a large number of sallow trees three years running, and have so far found that few that were deemed suitable in 09 and / or 10 are looking suitable this year. This may be due to the early spring, or the poor summer. Certainly, foliage growth varies a lot from year to year. I've even had some sallow trees change from being broad-leaved types in 09 to looking distinctly narrow-leaved in 11, and vice versa! Shape shifting... .
I need to ascend some sallows. It may be that more eggs than usual were laid this year on the sub-canopy isolated sprays that the insect generally favours.
Any excuse to climb trees... .