Nesting tray systems and tubes with removable liners allow you to remove the bee cocoons from their tunnels and examine them individually. When you separate the cocoons from the mites, parasites, and predators that may also be in the tunnels you can dramatically increase the percentage of bees that emerge in the spring.
How to Wash Mason Bee Cocoons: The best time to wash them is between the months of October and December. During this time period, mason bees will not emerge from their cocoon if held at room temperature. Open the trays or if you have tubes pull the liners and peel them, then separate the cocoons from the debris of pollen and mud used to plug the nest cells. Place the cocoons in a bowl of tepid water and gently move them around. The mud will sink to the bottom, and the cocoons will float. Let them rest in the water for 5 – 15 minutes. After that period of time, rinse the cocoons in a sieve until the water runs clean. Place the clean cocoons on paper towels to examine them. Look for little orange spots which indicate the presence of mites. Additional washing may be needed until you see very few mites. When the washing is completed, place the cocoons on dry paper towels and let them air dry for an hour or so. Scrub the nesting trays with warm water and let them air dry as well. Your cleaned trays will be disease- free and ready for nesting bees.
How to Store the Clean Cocoons: Store the clean, dry cocoons in a cardboard box inside of a metal container. Layer the cocoons between paper towels for cushioning and punch some holes in the metal container for air circulation. In February, place the cocoons in the “attic” of your bee house or in a box with a small hole from which they can emerge. Place the box near your nest blocks. Do not expose the cocoons to direct rain or sunlight, and protect them from predators. The bees will emerge from their cocoons and start mating and pollinating when the conditions are right.
This information is compiled from Pollination with Mason Bees by Dr. Margriet Dogterom. Please review her book for more information.