Candling Mason Bee Cocoons

   In addition to selling equipment and supplies relating to honeybees, we also sell equipment pertaining to mason bees. For the benefit of those unfamiliar with mason bees, they are a type of solitary bee which emerges in the spring, just in time to pollinate our spring tree fruit.  While not everybody is cut out to keep honeybees, just about anybody can do mason bees. They are easier, simpler and much less expensive. The big down side to mason bees is that they don't produce honey. They just help us have a good fruit crop.  As much as I love honeybees, the mason bees are much more efficient pollinators and will work in cooler and wetter conditions than the honeybees. In spite of having twelve beehives in the back yard, I didn't get cherries every year until I started keeping mason bees.

    We sell several different styles and sizes of mason bee housing, all purchased from BeeDiverse, a Canadian company located in Coquitlam, BC.  The key component of their mason bee housing is a stackable nesting tray.  I sell the BeeDivers nests because I use them at home and I really like them. I consider them a serious improvement over the homemade nests I previously used.  The main advantages to the use of the BeeDiverse stackable trays are their durability and the ease of harvesting the cocoons in the fall and preparing the nests for reuse the following spring.

    Every fall, sometime after September first and prior to Christmas,  I take apart the stackable nesting trays, remove the cocoons, wash them, candle them, and then store them in a cool place for the winter. I washed the cocoons several weeks ago.  The cocoons have to be washed first to remove parasitic pollen mites and in order for the candling to be effective. Today I candled the clean cocoons to make sure they were viable and that they weren't infested with parasites. That was kind of a long introduction to get to the topic of today's post.

Flashlight lens covered with cocoons

    I use the large six volt flashlight shown in the above photo to candle the cocoons. The flashlight lens has to be completely covered for it to work well.  Since our bathroom at work has no window that is a great place to candle the cocoons. I turn on the flashlight, shut the door and then I can easily see which cocoons I need to cull. Most of the cocoons that have too much light passing through are bad. Sometimes you can see the silhouette of an adult bee that stretches from one end of the cocoon to the other. This is actually easier to see in real life than it is in the photos.

    In the above photo you can see that two particular larvae failed to pupate.  They spun their cocoon, then died. The dead larvae are silhouetted as they lie curled up in one end of the cocoon. 

Cocoon parasitized by wasps

     In this photo lots of little cigar shaped objects are visible in one of the cocoons. That particular cocoon has been parasitized by a chalchid wasp. Most parasitic wasps are considered to be beneficial insects, but this particular wasp has chosen to attack another beneficial insect instead of a pest.

   I harvested 349 mason bee cocoons from four of my nesting blocks. I only had to cull 20 of those cocoons. I cut open about half of the culled cocoons in order to get some photos of the contents.  Most of my culled cocoons had larvae which failed to pupate. Culling out those cocoons would only be important if I were selling the cocoons. I don't leave my mason bee blocks out all summer. I usually take them down as soon as it appears that the bees are done with them. I put them on a shelve in the garage or take them down to the shop. Generally bad things are more likely to happen if the blocks are left outside. They might be discovered by a woodpecker or a flicker and predation by the parasitic wasps is very likely.  The reason I only found one of the cocoons with wasp larvae is mainly due to the fact that I took the blocks inside once the bees were done with them.

Wasp larvae from the culled cocoon

      At the top of the above photo you can see curled up mason bee larvae that failed to pupate. In the center of the photo there are about a dozen wasp larvae in an opened cocoon.  The adult chalchid wasp is about the same size as the larvae in the photo. The entire cocoon isn't as long as the nail on my little finger. Yet this little wasp has an ovipositor that can penetrate through a half inch of wood. They truly are amazing little creatures.