Osmia in Los Angeles Cty 2012

[KDouglas]

This was my third year of releasing Osmia lignaria and Osmia californica bees and it was to be the first year to set-up a sustaining lineage by not purchasing natal tubes from a vendor. I was satisfied with the results of the past two years. The bees seemed to like the location where I had put the tubes and had in prior years successfully repopulated clean tubes in that spot. This year I had 33 natal tubes set from 2011. I decided to let them stay outdoors in the habitat in which the females had populated them and not bring them in to hibernate in the refrigerator. The sad story is that all the bees succumbed to something. I did see one male in the spring but no other activity. I just finished investigating the cocoons and the majority seemed to have desiccated. When I open the cocoons the bodies fall out in pieces. It appears that a few did get out of their cocoons but could not make their way out of the tube and therefore died in the tube. In some cases it's clear that large pollen plugs (unsuccessful larvae? and they were still moist) were in the way. Most died in their cocoons. The soil around here has a lot of clay though my garden soil is quite loamy from composting and general vegetable gardening. What happened?

My thinking is that the winter was too warm and the bees simply dried out. Is that what others may be experiencing? Is there a species that should be able to overwinter successfully outdoors in the Los Angeles area?

Another thought is that the clay in the soil caused the plugs and partitions in the natal tube to be too hard to break through. It's a thought anyway.

Thanks so much for feedback. I'll be purchasing natal tubes again this year to start over.

KDouglas

[solitaryb]

Hi KDouglous - sorry that no one has replied to you earlier.

Let's do some forensic work - if I understand the timeline of events:
- Spring 2011: 33 (cardboard?) nesting tunnels blocked
- Summer 2011: remain outside
- Winter 2011/12 : still outside?
- Spring 2012 no emergence.
- Checked in April to discover different problems.

I have two questions:
1/ What sort of habitat held the bundle of tubes?
2/ What sort of temperatures are reached in the summer?

It can take between 2 and 6 weeks for a larva to eat its pollen - then up to 5 months for them to go through cocoon spinning phase and change into adults. A level of pollen phase incidents/larva deaths will occur (3 -8%), however high levels suggest heat-related conditions and larvae can be steam cooked.

As for leaving the tubes out later into the year, this leaves exposed them to the ecosystem that arrives from May/June such as solitary wasp parasites (Chalcid wasps) which will prey on the larvae spinning their cocoons. They are especially vulnerable if the tunnel walls are not very thick.
Holes along the tubes at the same position of the bee cells, are a sign of the first of two generations of Chalcid wasps creating an exit hole and emerging and spreading to the other tubes and cocoons that their mothers didn't initially reach. This condemns pretty much all of the cocoons in a given nesting tunnel. The second generation will over-winter hidden in relatively normal looking but slightly shrivelled cocoons. Multiple wasps will then burst out at the end of the following spring to repeat the.

You pretty much spotted that if a bee emerges from behind a dead cell, it may just never emerge. So you have to check and free these healthy cocoons from the tubes in the Autumn/fall.

Finally, if you've left out your tubes over the winter rather than taking them inside, all sorts of humidity issues will develop, especially if the habitat you bought is thin or inadequate for sheltering them from exposed conditions.

If we want to manage artificially these insects, we have to be aware of the risks associated with our materials and methods. Hope you have a better year in 2013.

[KDouglas]

Thanks for the response. After slicing all the tubes open and examining the contents I came to the conclusion that somehow the environment must have become too dry. I found many fully formed bees that apparently were not able to dig their way out. The mud walls were quite hard. The soil here has a lot of clay. However I compost and vegetable garden so there is plenty of loamy soil. It was very discouraging especially when the previous year had gone so well. I didn't get any this year. I use mason bee homes from http://masonbeehomes.com/ and started with natal tubes from knox cellars. The first two years it worked well and then in 2012 I decided to not get more larval tubes and just let the population I had acquired continue. I didn't retrieve the blocks in to hibernate in the refrigerator. The homes are mounted under the eaves on the southside of the garage. So they are well protected from weather.

Hearing finally from someone is encouraging. I'll try again by purchasing natal tubes to start. My goal is a continuing, self-sustaining population. So, it shouldn't be necessary to bring them in to hibernate. But perhaps it is. Your thoughts are welcome.

Thanks so much.
K. Douglas

Hi KDouglous - sorry that no one has replied to you earlier.

Let's do some forensic work - if I understand the timeline of events:
- Spring 2011: 33 (cardboard?) nesting tunnels blocked
- Summer 2011: remain outside
- Winter 2011/12 : still outside?
- Spring 2012 no emergence.
- Checked in April to discover different problems.

I have two questions:
1/ What sort of habitat held the bundle of tubes?
2/ What sort of temperatures are reached in the summer?

It can take between 2 and 6 weeks for a larva to eat its pollen - then up to 5 months for them to go through cocoon spinning phase and change into adults. A level of pollen phase incidents/larva deaths will occur (3 -8%), however high levels suggest heat-related conditions and larvae can be steam cooked.

As for leaving the tubes out later into the year, this leaves exposed them to the ecosystem that arrives from May/June such as solitary wasp parasites (Chalcid wasps) which will prey on the larvae spinning their cocoons. They are especially vulnerable if the tunnel walls are not very thick.
Holes along the tubes at the same position of the bee cells, are a sign of the first of two generations of Chalcid wasps creating an exit hole and emerging and spreading to the other tubes and cocoons that their mothers didn't initially reach. This condemns pretty much all of the cocoons in a given nesting tunnel. The second generation will over-winter hidden in relatively normal looking but slightly shrivelled cocoons. Multiple wasps will then burst out at the end of the following spring to repeat the.

You pretty much spotted that if a bee emerges from behind a dead cell, it may just never emerge. So you have to check and free these healthy cocoons from the tubes in the Autumn/fall.

Finally, if you've left out your tubes over the winter rather than taking them inside, all sorts of humidity issues will develop, especially if the habitat you bought is thin or inadequate for sheltering them from exposed conditions.

If we want to manage artificially these insects, we have to be aware of the risks associated with our materials and methods. Hope you have a better year in 2013.

[solitaryb]

After slicing all the tubes open and examining the contents I came to the conclusion that somehow the environment must have become too dry. I found many fully formed bees that apparently were not able to dig their way out. The mud walls were quite hard. The soil here has a lot of clay. However I compost and vegetable garden so there is plenty of loamy soil.

The bees will take the soil they want and the clay content is ideal. As the inner walls of the nest structure are pretty thin, the digging out issue is unlikely. In those that you cut open, what you didn't mention was what was just in front those that died. It may be that the obstacle of a parasite or one dead bee stopped all the rest behind them. Another other possibility is that if you have mild winters (like many of us did in the Northern hemisphere last year) and/or you bought a sub-species of bees from another colder state or climate - they may have woken up too early and used up their reserves of fat whilst in the tubes and thus just starved to death before their triggers to emerge occurred.

It's why I would counsel a 'local biodiversity first' approach so that you don't buy cocoons, but start with empty tubes for nesting. So that you raise mason bees that are adapted to the climate and flying round Los Angeles. I am sure that the grand-daughters of some of the bees that you released in the prior two years will happily take up residence.

My goal is a continuing, self-sustaining population. So, it shouldn't be necessary to bring them in to hibernate.

I keep saying this to people that want to have a good population of mason bees or even leaf-cutters, is that the bottom line is that you are trying to help replace the diminished natural habitat where there are fewer and fewer nesting sites and you are concentrating these bees in artificial ones. In doing so you can't escape the responsibility - that you have to take the decision as I call it. You have to decide to:

1. have artificial nesting habitats that are designed against parasite entry where possible,
2. you have to have a timeline strategy to protect the bee larvae and cocoons at certain periods where they are at risk from wasps or extreme exposure, and
3. you have to actively manage the bee tunnels off-season to enable the maximum number of healthy bees to emerge in the spring.

These gestures are very few. The benefits are great. I went from 100 cocoon/bees emerging in 2009 to 2500 emerging in the next 4 weeks. Take the decision and make your luck.

[jeroenverspuij]

Dear colleagues,

I am looking for an HD movie with close up of the Osmia Rufa or other Osmia bees which crawl in or out of their nest in a wooden / bamboo stick. Youtube videos are not suitable.
Who can help me?

Sincerely,

Jeroen Verspuij