There is a very severe threat to our Mason Bee populations, Chalk Brood. According to the USDA Agricultural Research Service there is very little known about the actual fungus in the genus Ascosphaera that attacks the Blue Orchard Mason Bee, Osmia lignaria. What we do know is that it is highly contagious and deadly, it can wipe out your entire colony. Larva ingest a deadly spore and vector the disease to any bees that come in contact with the cadaver. These infected bees spread the fungus to your mason bees house, flowers and other nesting sites.
As many of you know our Mason Bee sales/fundraising program has been halted for the season due to this devastating disorder. After sampling tubes from our arboretum and tubes from several different mason bee donors we found that all of our populations had varying degrees of infestation. We have worked tirelessly to replace tubes that had already been sent out and have opted to stop selling cocoons for the year. Our donors have gone through a very tedious process of harvesting and sanitizing their remaining cocoons, in hopes that an uninfected generation will be born this year.
Please take this threat very seriously. This is just a great reminder of the importance of sanitation in your orchard practices. The only way to ensure that we are not spreading the disease is to harvest all of your mason bee cocoons. Clean and sanitize all of your nesting sites/homes on a yearly basis. Put out clean tubes every year, never reuse old tubes.
Harvesting cocoons takes a bit of time but, saving these bees is well worth our time and effort. Once the cocoons are harvested, by carefully slicing or cutting open, you must remove all the frass and pollen debris. 1.5 tsp of bleach to 1 cup of water is the recommended solution for sanitizing the cocoons and their homes. Your cocoons must be dried and placed in a refrigerator in a vented container. Temperature and humidity are important factors for their survival. 36-39 degrees and 60% or ^ humidity is ideal. A “bee emergence shelter” will need to be placed as close to their new nesting site as possible. They are available from different online sources or you can make your own. It needs to be a dark container with holes. At the arboretum we have used things like sour cream/yogurt containers and small waxed cardboard boxes.
Lots of information and control measure can be found online, please educate your selves on this disease and other problems that threaten our Mason Bee populations.
I wish you all the best of luck and remind you that we need to be good stewards to these wonderful little creatures that have served us so well over the years.
HOS Arboretum, Manager