In
May and June of 2010 and 2011, I collected wild bees from 24 blueberry fields
in Hancock County in the towns of Orland, Penobscot, Sedgwick and Blue
Hill. By "wild" bees I
mean any bee that is not a honeybee or a commercial bumblebee. Most of the wild bees are native,
occurring naturally in Maine, but a few are not native and have been brought
here by humans at some point in time.
The wild bees are generally small- the size of a honeybee or less. The wild bees are mostly solitary,
living individually or maybe in aggregations, but never forming the large
colonies seen with honeybees.
Naturally occurring bumblebees are wild, and they live in fairly large,
social colonies, but I did not collect bumblebees. In the spring the only bumblebees that are out in the
blueberry fields are the queens that are foraging for nectar and pollen before
starting to lay eggs. If I collect
a queen, I prevent the founding of an entire large colony of bumblebees. I did not want to do this, so I avoided
collecting bumblebees whenever possible.
I
used two methods of capture. The
first method involved placing small, colored cups filled with soapy water in
the fields for 24-48 hours. This
method catches anything attracted to the cup, including plenty of insects that
are not bees (and unfortunately slugs like the cups as well). Many of the bees I've caught have come
from these cup traps, but just because I catch a bee in a blueberry field
doesn't mean that that bee pollinates blueberry flowers. So, I also caught individual bees found
foraging on blueberry flowers. From
these bees I have made a list of possible wild bee blueberry pollinators.
A field assistant shows how to hand-catch bees on blueberry
flowers- taken in Addison ME, 2012.
This list includes 223 individual bees from 34 species
caught on blueberry flowers.
More than half of these 223 bees come from only three species:
Andrena carlini
Andrena
vicina
Andrena
carolina
The Andrena are
ground-nesting bees. The adults
dig a main burrow and create lateral burrows for the cells. They coat the walls of the cells with a
waterproof lining to protect the eggs and larvae. In each cell they place a food mass (mostly pollen, but some
nectar drops might be included) and one egg. The pollen is the food for the growing larva and sustains
the bee until it reaches adulthood.
Almost all Andrena overwinter
in their cells as adults. Most Andrena make individual nests and don't
share entrances with other adults.
They may place their nests near others. I have seen this in one blueberry field that had a southern-facing,
sandy slope. Early in May when the
blueberry flowers were just opening but no leaves were out, I came upon an
aggregation of Andrena nests on this
slope.
Below
is a bee at the entrance to a nest.
It is not one of the three species listed above, but it is a similar
size. The bee is about 3/4 an inch
long and the hole not much more than 1/2 inch in diameter. This nest was located in a small, sandy bare
patch in the middle of the blueberry field.
These
three species of Andrena might be
quite important for blueberry pollination. In general, in 2011, in the fields where I caught the
greater number of the Andrenid bees, the fruit set also was higher.
