I have examined these mites (mag x 100) and noticed that the active mobile ones where mainly either trapped inside a cell full of them en masse or in the same cell as a fully formed cocoon. They all had a pinkish triangle shape on their backs with the point of the triangle pointing towards the head, then a pale elongated gap from left to right on their backs then another pinkish section/plate? at the rear. Their legs were all a deeper pinkish, with numerous short stubbly bristles. However their two rear legs had huge long fine and very thin slightly curved appendages. During the cleaning process I examined them and found in some cases these had actually become entangled in the fine strands of cocoon silk.
I have looked at microscope photos of Chataetodactylus osmia and photos of C. krombeini and the patten re pinkish shapes and long rear appendages I have described looked, to me anyway, more like the latter than the former.
The pearly white mostly immobile mites were to be found mainly on the edges of several cell as well as inside some cells that had no cocoon, only a pollen ball, or in cells that contained no pollen ball just pollen grains.
I found one cocoon partially open, where a female would usually have been as it was the innermost cell. This cocoon was small in size than the usual female sized cocoons, although that could be that it was a small female deprived of food by the mites, or a misplaced male.The bee was shrivelled and wrinkled around the head I suspect it had been eaten. It was a whitish/yellow colour. It was also very small and was very dead.
last year I had 2012 red mason bee cocoons, with males emerging on 2 May and females on 21 May 2012, this year I start with 109 cocoons, with some more to view and clean in the next few days or so.
See video here..... http://bit.ly/WuJdEq
Cheers George Pilkington