In reply to coaster:
Two weekends ago there were (amazingly) none in the forests of Rothiemurcus on a warm, humid, windless cloudy afternoon.
Last weekend at 1000m on Bynack More the temperature seemed to drop from too-hot-for-midges to too-cold-for-midges over the course of about half an hour, and we were only troubled by a couple of them.
That might be good news for you in the cairngorms, or might be a sign that they have just now hatched and will be out for your blood...