[NAFEX] Orchard Bees Hardiness

derry and bill wchase at interchange.ubc.ca
Sat Apr 16 11:58:58 EDT 2005


I've gone through my file on Blue Orchard Bees (BOBs), plus I re-read 'How to
Manage the Blue Orchard Bee for Orchard Pollination' by Bosch and Kemp and there
is no information on how cold is too cold for BOBs.

The Bosch and Kemp book is a summary of the research done on the BOB at the Bee
Biology lab in Logan, Utah. They overwinter their BOBs at 3-5°C (39-41°F).
p12: "the duration of this dormant period depends on the local climatic conditions
of each zone and the origin of the population."

p 25: "The conditions (mainly temperature) to which BOBs are exposed during
development, pre-wintering and wintering are extremely important, as they not only
affect survival, but also vigour, time of emergence, establishment, and ultimate
nesting and pollinating performance."

In some information I got from Dale Nielson (a wild bee specialist in Logan Utah
who is probably on this list), he writes that in Northern Utah at 4200' elevation,
the overwintering cocoons are hardy to -15°F. In Western Oregon at <100'
elevation, the overwintering cocoons are hardy to 20°F (that's +20°F!).

In a map, Dale shows the known range of BOBs in the US (the boundaries of the
States are not shown so I'll have to extrapolate). The western strain occurs from
the Pacific Ocean eastward to include Montana, Wyoming, Colorado and New Mexico.
The known range in the US of the eastern strain of BOB is from the Atlantic west
to include Minnesota, Iowa, Missouri, perhaps Arkansas, Tennessee, and N Carolina.

So, with this limited information, I'd say you'd have been better off to
refridgerate the BOB cocoons until about two weeks before apple bloom.

But also, wild BOBs do occur in Minnesota so they must survive the -40°F temps,
but maybe winter mortality occurs to reduce the population.

I recommend the book by Bosch and Kemp. I sell it (see web address below) and you
can probably get it from your local university book store.

I leave my BOBs out-of-doors here in south coastal B.C. and the temps can drop
to -15°C (5°F), but not often. I measure the % emergence and I'm getting about 98%


~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~  ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~
Derry Walsh & Bill Chase
wchase at interchange.ubc.ca
Aldergrove,  B. C.,  Canada
phone/fax (604) 856-9316
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Home web pages: http://derrysorchardandnursery.ca
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I kept them overwinter in an enclosed shed. I would guess the bottom
temp. in it
: was minus 35 or so.  What is their bottom temp hardiness?
 Any chance they are still alive?
: Del, N. MN Z 3

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