If you are increasing your mason bee population by providing nesting houses, early October is the time to remove the nesting tubes and clean the houses with water and a bit of bleach to kill the mites that may be overwintering.
Remove your cocoons from the nesting tubes and gently rinse them with water. Use a sieve and water only, no soap or bleach. Put the cocoons on paper towel until perfectly dry. The mites that kill the bees are brownish red. There should be no stain on the paper towel. If there is repeat the rinsing process.
This might be a good time to sort the cocoons into male and female. It will be important to know when you put them out in the spring. That is if you are dividing the cocoons and dispersing over your yard. The female cocoons are usually larger. It seems not too difficult to tell. We will see how successful I was in the spring.
To keep the cocoons safe over the winter, the clean and dry cocoons should be stored loosely surrounded by paper towel. Perhaps some cardboard underneath (keeps them off the cold metal), in a metal container with air vents punched in the lid. I am using an old cookie tin. The tin should be stored in a cool place such as a garage or other outbuilding where it will not freeze.
The metal container is necessary to keep the mice and such at bay and the vents are necessary to keep from smothering the little bees.
Think about bringing them out when the Pieris bloom.
Photo By USGS Bee Inventory and Monitoring Lab from Beltsville, Maryland, USA – Osmia conjuncta, F, MD, back_2015-11-20-21.40, Public Domain