Bees

Leafcutter bees are great summer pollinators.    It is easy to start with these bees.  All that is required are bee cocoons, a suitable nest and some hot summer weather.

Many of our customers have started their new hobby with these great little summer pollinators.  But it was not clear how long these bees needed to develop into adults and emerge in the summer.  We heard of people throwing them out, cutting them open and finding  a fleshy grub that does not look at all like a bee!

Here are the facts.  Under laboratory conditions and inside an incubator at 30C, bee pupae need 20-31 days to emerge as adults!

This is a long time!  This means that under normal conditions (and about half the time it is night and temperatures are cooler)  the emergence time is much longer than 21-30 days.  Under any natural conditions, emergence is more like 30-45d+.  They say ‘Patience is a virtue’!

Twenty two species occur in Western Canada.  Megachile rotundata is a species of leafcutter bee that originates from Eurasia.  It is used in the commercial seed production of alfalfa.  The female Megachile rotundate has silvery gray hairs on the underside of its abdomen.  Other female leafcutter bee species usually have golden, tan, or black hairs on the underside of their abdomen.

Megachikle rotundata overwinters in the pre-pupa stage. during last spring and early summer, temperatures are sufficiently warm for pre-pupae to develop into adults.  Then adults emerge to pollinate our summer blooms.

Nesting material for leafcutter bees were first made out of grooved wooden pine boards that were stacked to make a series of nests.  Polystyrene grooved boards and nesting holes molded into solid polystyrene blocks are both used today.

In part, excerpted from our book ‘Pollination with Mason bees” page 100 by Dr. Margriet Dogterom.  Get yourself a copy as 25,000 others have done.  It is the standard management guide for mason bees and includes details about other bee species.

With every technique and system there is a good way to do it and there is a not so good way to do it.  It is the same for various techniques used to safely overwinter bee cocoons.  There are 3 main things to keep in mind when storing mason bees:

• Keeping predators from eating bee cocoons
• Preventing bee cocoons from drying out
• Preventing bees from coming out earlier  and or in the wrong place (like a storage shed)

The easiest way to keep rodents away from eating the cocoons  is to store them inside a fridge.   To keep cocoons from dehydration inside a fridge place cocoons into a Humidity cooler.  But do check for water inside the Humidity Cooler.  An alternative is to store them outside.  If outside storage is preferred, keep cocoons in a cookie tin with a few air holes in the lid.

Adding water onto a pad to keep cocoons moist.

The metal tin will prevent predation.  Outside storage only works however until temperatures warm up.  The cocoons will have to be moved to the mason bee home for release as Spring arrives.  Releasing them from a Castle or other home will make sure the bees emerge at the right time at the right location.

A small fridge with manual defrost is the best fridge for storing mason bee cocoons.

Tony W. writes  “I found insect pupae embedded by fluff this winter. There was also a stash of plant pollen also wrapped in plant fluff. A cavity in a timed water valve was completely filled by these items. I see that there have been comments on your blog mentioning these. I have come up with an answer as to what these are. I believe they are wool carder bee pupae. I damaged some of them trying to figure out what they were but have four left with one in quite good condition. With luck an adult will emerge and I can reach a firm conclusion. However, the descriptions of overwintering by these bees fits what I found quite well. ”  see link   http://www.nativebeeconservancy.org/native-bees/wool-carder-bees/               There are several articles and posts about this bee.  This picture is from another blog post.  To see other articles about this bees use the search window in the upper left corner of this blog and use the word-   cotton   You will find  additional articles with pictures .  Dr Margriet

Hi Margriet,

The first thing I want to mention is that I did compare your Canadian leafcutter bees to some leafcutter bees purchased in the United States. I incubated both sets of bees under the same indoor conditions where the leafcutter cocoons were placed in plastic petri dishes with a plastic lid that holes drilled in it for air circulation. I also had an internal temperature probe in each dish to monitor the temperature, and both temperature and humidity were recorded on a daily basis to an Excel spreadsheet. I also took notes and put them on the spreadsheet as I examined a few cocoons over the incubation period.

Emergence:

My results on leafcutter bee “emergence” rate would support what has already been published in the literature (see PDF). That is, under my incubation conditions I found that the Canadian bees were much better than the U.S. leafcutter bees in the percentage of bees to emerge. That is, I had 99% of the Canadian leafcutter bees as compared to only 55% of the U.S. leafcutter bees emerged over the same time period.

The other thing that I found, which I would do different next time, is that the required temperature of 86oF (30C) for the bees to emerge by 28 days is probably very critical. When I received both your bees and the U.S. bees at the end of May, I decided to try and incubate them inside my house where the temperature is more constant. During May and June in the Portland area we still have wild swings in temperature where it can be 64oF (17.7C) for many days or weeks in May and June.

With the indoor incubation I was only able to maintain an average daily temperature of 76F (24.4C) as compared to the needed 86oF (30C), which resulted in the bees only beginning to emerge (the males) at 30-32 days instead of the standard 18-20 days. Fortunately when the first males began to emerge I put them all outside and our daily temperatures were then in the 80-85F (26-29C) range. Again, despite the longer incubation time I still had nearly all the Canadian bees emerge as compared to only about half of the U.S. bees emerge over this same time period.

Retention:

The retention of the leafcutter bees was a surprise to me in that only 5% of the Canadian and none of the U.S. leafcutter bees decided to take up residence in my nesting box area.

Where I put the bees for release was actually within the middle portion of my Mason bee nesting structure (that faces East), and it contained many empty round tubes with and without papers liners, two of your corn stacked-systems, and many of the natural reeds at various sizes.

Also, on the other side of my nesting box are rose bushes, a big lilac tree, azaleas, a redbud tree, and many other plants that leafcutter bees are supposed to like for nesting material. We also have a very large Wisteria plant that actually hangs near my mason bee nesting area, and I could find many of the leafcutter bees on the Wisteria flowers as well as on other flowers all around my house. However, despite being in close proximity to my nesting box on the flowers that very few bees decided to take up residence. Wherever the bees decided to go I hope they survive the winter and come back next spring.

I am curious though what you or others have done to have good retention of leafcutter bees?

Anyway, it was very fun to have them as summer bees, and I definitely would order more leafcutter bees from you next spring and try a few different things. I have also taken a lot of video of the leafcutter bees on our flowers, and when I have time I plan to process the video to extract some still photos to send to you.

Best regards,

Michael, WL Oregon

Thank you Michael for sharing your findings.  The Abstract from the scientific article is given below.  Dr. Margriet

Emergence success and sex ratio of commercial alfalfa leafcutting Bees from the United States and Canada

J. Econ. Entomol. 98(6): 1785Ð1790 (2005)
ABSTRACT Samples of overwintering alfalfa leafcutting bee, Megachile rotundata (F.) (Hymenoptera:  Megachilidae), cells were sent to the laboratory as loose cells or in nesting boards from bee
managers in the United States and in Canada. X-radiographs of cells were used for determining cell
contents. Cells containing live prepupae were incubated, and the sex of emerging adults was recorded
daily. Cells from which no adult emerged were dissected to determine the developmental stage of dead
bees and sex of dead pupae or adults. Bee cells incubated in commercial settings and placed in alfalfa
fields by the same bee managers described above also were evaluated to determine adult emergence
success. The proportion of live bees in wood nesting boards from the United States was much lower
than the live proportion in polystyrene nesting boards from Canada and loose cells overwintered in
the United States. For laboratory-incubated loose cells, survival and sex ratios of bees from Canadian
sources were statistically higher than those of U.S. bees, but the onset and duration of emergence times
were similar. Fewer bees survived in the commercial setting than in the laboratory. Prepupal mortality
was signicantly higher than pupal or adult mortality, but there was no significant difference between
the sexes in the likelihood of survival during incubation. This study supports the commonly held belief
that alfalfa leafcutting bees raised in Canada and then sold to the United States represent a more viable
source of bees than most bees produced in the United States.

KEYWORDS: Apiformes, Apoidea, Megachilidae, Medicago, lucerne

Bumbler IA

Bumbler 2



Queen



Honey on base of tubes

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.

Roeland’s mason bee web site


Mason bee se-up while pollinating cherries. Mason bee nests are made of routered channels cut out of compost board. Boards are held together with a tie-strap.



Osmia rufa doing the finishing touches to her nest.



Osmia rufa male.  Note the long antennae.



Females resting over night inside their nesting tunnels.

Embrace (Osmia rufa)

Fierce competition

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