Frank mentioned removing mites with a ‘large stainless steel colander’. The best colander is not just any colander. More about this later, but first, lets back up a little and I will explain my rationale for removing mites.
Getting rid or removing ALL mites from cocoons is difficult. I think the main aim is to remove the majority of mites, so that mason bees have a better chance of producing healthy offspring. Even if all mites are removed from harvested cocoons, there will be the occasional mite covered wild bee that arrives from within the local wood. These mites are spread successfully ensuring mites are always around. The best that anyone can do is to remove the majority of mites from harvested cocoons. This give mason bees a better chance in producing healthy offspring rather then mites.
Washing with water, removes adhering frass and the majority of loose mites. After washing, there are still lots of mites in amongst the threads of the cocoon.
These mites are best removed by friction. I have found the most successful way to remove these mites is to gently roll them over a METAL window screen stapled to a frame. Another way is to gently roll them around colander with a metal screen (NOT PLASTIC, NOT STAINLESS). Plastic and stainless steel do not have the abrasive quality of metal screen.
This can be done in two stages. First wash with the appropriate colander under and in running water. Second, when cocoons are dry, roll them over another screen to get the remaining mites off.
I have just finished washing my OMB cocoons.When examined with a 10X magnifier, I saw about 50 mites on the outer surface of each cocoon. 2 baths in bleach and water (.05%) killed most of them.
However, these mites are not pinkish but greyish with a cream stripe across the back. Is this a different species?
Removing the majority of mites is done by first washing cocoons. It is especially effective if done under running water while coocoons are in a colander. The friction of the screen of the colander will remove most mites. As far as I know, bleach does not kill mites. It might irritate them and then are more easily removed from the cocoons…. The white stripe on the mites indicates they are adult mites. All the other mites are immature forms or mite eggs. I do not know if these might be a different species.