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Osmia californica

Michael emailed me with a question on setting out new nests when the old nests are getting filled.  He asked if adding a nest close to the others would disorientate the bees already nesting at the location.  
I suggested that additional nests are best set out in the visual range and clustered close to the original nests. 
Michael also noted that his bees headed for the tubes first.  Yes mason bees prefer round holes, especially when the substrate is wood or carboard.  Unfortunately the bees’ choice is not always the best for eaze of management. 
Michael’s original question was:
If I need to set out more nesting sites for the Mason bees should I put them next to existing sites, or, put them a bit away from the one’s I originally set out?  The reason I ask is that I am getting many more bees to nest so far this spring compared to last year but I do not want to mess up the bees visual cues to the old sites.  I also know they like to be near each other.  Your thoughts?
Michael’s follow up notes are:
As I mentioned before I was particularly surprised by what happened this spring when most of the O. lignaria emerged at once with a very low dispersal rate.  This activity was in contrast to the last two springs where the dispersal rate was high and emergence rates were very sporadic.
In my nesting set-ups, which I have two of them around my house (see the BEFORE photo), I put 40 cocoons in the wooden house, and 20 cocoons in each of the tube units (80 total of O. lignaria).  There was also 20 of your O. californica cocoons in the wooden nursery house.
I set out all of my bees on April 20 and to my astonishment, almost all of O. lignaria had emerged by April 22, and the first mud nests were made in the tubes on April 24.
The second surprise was that all of the bees decided to move to the tube units (reeds and paper filled tubes).  This is where I was beginning to get concerned that I would not have enough nesting sites.  We had a week of very good weather, and then we had four-five days of cool and damp weather which I then decided to put another tube unit below the existing two tube units (see AFTER photo).
During this cool period of weather, I noticed that all the O. lignaria bees were resting in the tubes, so I kept track of what bees were in what tubes and how far they had gotten along in building their mud nests.  The good news is that when the good weather returned last weekend that all of the existing bees resumed their normal activity and were not deterred by the NEW unit below!  It seems that putting a new nesting house nearby did not distort their visual cues (at least under my conditions).
Also, in taking the pictures of my nesting sites last weekend I noticed the O. californica I purchased from you were beginning to emerge.
I just managed to snap a photo of a O. californica male and female bee doing what a pair of bees are supposed to do .
It might also be my imagination but it appears that the O. californica seem a bit larger than the O. lignaria, and so far all the O. californica bees are headed for the tubes.
Maybe it is some kind of social communication or interaction, but who knows what the bees are really thinking!
Best wishes,
Michael-
Mating Osmia californica

Before
After

Osmia californica comes out late in spring, often their emergence overlaps the latter end of the Osmia lignaria (early spring mason bee) season.

However very little is known about them.  If you’d like to share your photos of Osmia californica, please email them to me and I will get them on this blog.

I had to go to my old stomping ground to get this article.  In 10 years Simon Fraser University did not seem to have changed much- although I did only go to the library.  It is a short ride from my home and so tonight I thought to chase up the 1966 article by Levin.  I wondered into the library, walked up to the 5th floor and found The Journal of Kansas Entomological Society.  Just like that!  I spent a lot of my time in amongst these rows and rows of journals.  So it was not surprising that I found the green volumes so quickly.  Unfortunately there was no volume number 39.  I went to information and a kind gentleman looked to see if the library had it hidden from my view.  No, but library did have it in digital format.  Perfect!  It was fairly simple to search for it on the computer and get it printed out.  Parking for 55mins was $3.25!  But enough about my adventure. 

Here is what Levin had to say about Osmia californica.  Levin compares Osmia lignaria with Osmia californica.  I will focus on the details of Osmia californica.

Osmia californica
-Restricts pollen collection from a few composites
-Does not always overwinter as an adult (lignaria overwinters as an adult)
-About half of 33 overwintering cocoons were prepupae and the remaining half were adult
-Uses a mixture of mud and small amount of leaf tissue (lignaria uses mud only)
-Leaves no vestibule at entrance to nest (lignaria leaves a vestibule)
-Seals last cell with a thicker partition and does not build an end plug
-Buries its egg within the pollen mass (lignaria lays the egg on top of the pollen mass).

I think the most interesting part of this information is that Osmia californica does not always complete their transformation into an adult bee by winter.  This means that some bees overwinter as prepupae and complete their development the following spring.

The Wasmann Journal of Biology  (Vol 32 no 1 1974) has an excellent article on a variety of bee species including Osmia californica.  It includes range maps of Osmia species. The known distribution of Osmia californica is in western North America and eastwards to Montana and Colorado (including British Columbia, Washington, Oregon, California, Idaho,Wyoming, Utah, Nevada) but not in Arizona or New Mexico. 
Female color is metallic blue black, legs black to reddish black.  The mandibles have 4 teeth.
Male is black to metallic blue black. 
The male and female varies from entirely black to black with white tufts and areas of intermixed black and white.
It appears as early as May in the southern and warmer location and as late as August in higher altitudes.

Biology:  The egg is located in the center of the pollen store, with the store usually filling the cell.  The cell and plug partitions are constructed of small pieces of masticated leaf and mud.  The amount of leaf varied from 1% to 50% of the partition.  The partitions were tough, with the outer surface shallowly concave and smooth.  The inner surface was rough and the spiral ring construction was easily seen.

Finding anything written about Osmia californica is not easy.  Although I found an article written on californica by M. D. Levin, his scientific article was published in the Journal of Kansas Entomological Society, 1966.  Unless you are affiliated with a university, only the abstract is available.  I will write a summary of the article when I get the full article.  But I did find a great web site with good and very detailed photos of Osmia californica.  Link to photos of Osmia californica

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