Nesting tray systems allow you to examine each tunnel and check on the state of your mason bees. By removing the bee cocoons, you can wash them and remove all debris and mites that may be in the tunnel.
How to Wash Mason Bees: The best time to wash mason bees is between the months of October and December. At that time of year, mason bees will not emerge from their cocoon if held at room temperature. Open the trays and remove the cocoons from the debris of pollen and mud used to plug the nest cell. After removing the cocoons, place them in a bowl of tepid water. Gently move them through the water. 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 are a sign of 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. Puncture 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. They will emerge from the cocoon 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.