AHB is not stalled at the border in California as some have suggested.
They are all over the Imperial Valley, and progressing steadily toward the
L.A. basin. They are likely to arrive there this coming season or the one
following.  L.A. is at about lattitude 34.
 
It appears that AHB is limited by certain factors, such as winter
temperature and absence of a steady year round food supply. It has been
suggested that lattitude 35 is a sort of boundary line beyond which these
conditions aren't met consistently enough to support AHB.  However, there
is a climatic band just inland from the California coastline that has me a
little concerned (especially since I live in it).  This area runs all the
way up to the south San Fransisco bay area.  It rarely ever freezes, there
are abundant winter blooming plants, and the landscape is dotted with
small, medium, and large cities.  The cities are what have me wondering
most, because cities in warm climates are never without a nectar flow.
Urban plantings are so diverse, and are generally selected for bloom
potential to such a large extent that bees are rarely without a steady food
supply.  It seems to me that this urban phenomenon might simulate tropical
nectar flow conditions.  I keep my bees in a rural setting and have about 2
months of near total dearth in late fall and early winter, but I have
several friends with bees in the San Jose area who pull a box of honey off
of their best hives every month of the year.  (Finding a time to treat
these hives for mites is a real problem, by the way!)
This makes me wonder if AHB could get a foothold in cities near the
California coastline well above the 35th parallel.  (San Jose is just above
lattitude 37.)
 
Any ideas?  Is there any other urbanized coastal area near the north or
south 35th parallel with AHB exposure for comparison?
Michael
Michael