The Leafcutting Bee
RICK AMES
Seed Production Agronomist
W-L Research
Successful alfalfa seed production
requires a pollinator. The three major
pollinators used in commercial alfalfa
seed production in North America are
the alfalfa leafcutting bee. the alkali
bee, and the honey bee.
The alfalfa leafcutting bee. Mega
chile rotundata, is often considered
the “best” alfalfa pollinator for rea
sons outlined below. Even at an an
nual cost of $l5O-200 per acre, it is the
pollinator of choice in many alfalfa
seed production areas.
However, there are a number of in
sects, diseases and other pest prob
lems unique to the leafcutter bee
which can negatively impact this pol
linator.
A Managaeable,
Proficient Pollinator
The alfalfa leafcutting bee is a very
efficient pollinator of alfalfa. This bee
aggressively works the flowers, caus
ing them to trip and release pollen
which the bee collects and transfers
from flower to flower.
The leafcutter bee’s four to six
weeks of pollination life allows plenty
of time for large numbers of flowers to
be pollinated, resulting in high yields
of seed. One female can pollinate up
to 10,000 flowers, yielding up to V*
pound of seed.
Controlling where the bees will pol-
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linatc is accomplished by placement
of bees in or near a target alfalfa field
which has plenty of desirable bloom.
They will quickly nest in trailer
mounted, man-made domiciles, mak
ing movement between fields possi
ble.
Since the alfalfa leafmtting bee
prefers to work close to its nest, it will
not leave the field if conditions are
good. Also, alfalfa bloom is by far its
favorite source of pollen and nectar,
so competition from other crops or
weeds is not a problem.
Threats To Leafcutter Health
There are many parasite and preda
tor problems that attack the alfalfa
leafcutting bee. These include parasit
ic wasps and predacious beetles. How
ever, the alfalfa leafcutting bee is very
sensitive to insecticides, and few in
secticides have been found that pro
vide control of alfalfa seed insect pests
with minimal losses to the leafcutter
bee.
There are also a number of diseases
that infect the alfalfa leafcutting bee.
The worst disease is a fungus called
chalkbrood that attacks the larval
stage of the bee. Some birds can also
cause significant loss by feeding on
the adult bees. These pests can all be
held to manageable levels by use of
cultural, chemical, or biological con
trol methods.
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Foraging Around, Lancaster Farming, Saturday, July 11, 1998-Page
Alfalfa’s Premier Pollinator
Determining Larval Health
Through X-Ray Photography
Accurately determining the num
bers of leafcutter bees available for
pollination is accomplished through
quality evaluation of the bee larvae
during the winter. Bees on hand are
first evaluated to determine actual
numbers of live larvae. If mote bees
ate needed, they are purchased in the
larval form. Each larva is encased in
its own cell constructed primarily of
leaf material. A particular cell must be
cut open to evaluate whether healthy
or dead larvae are inside.
Another method is by X-ray, which
will show what is inside the cell with
out manually cutting it open. The X
ray method is faster and easier when
Dairy Graziers Not Exempt
From Expansion
COLUMBUS, Ohio - Switching
to intensive grazing could delay the
need for dairy farmers to expand,
but not forever, said Tom Noyes,
dairy agent at the Wayne County
office of Ohio State University
Extension. *
Changing from a conventional
dairy to intensive grazing has the
potential to increase a dairy
farmer's profit per cow by $3O to
$5O. For a 100-cow dairy, this could
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looking at hundreds of cells in a single
sample of a particular lot of bees. The
X-ray will reveal live larvae, dead lar
vae, immature larvae, parasites, and
pollen balls.
Knowing the number of live larvae
in a sample makes it possible to calcu
late how many bees can be expected
from a particular lot.
Summary
The alfalfa leafcutter is the pollina
tor of choice in many alfalfa seed pro
duction areas.
There are many factors which im
pact the health of leafcutter bees, but
the use of X-ray photography can al
low growers to accurately determine
how many healthy pollinators will
emeige from a lot of cells.
mean a $5,000 per year increase m
income that could maintain a dairy
farmer's current standard of living
for five to 10 years.
But, if profit per cow is not
improved in other ways, cost of liv
ing increases eventually will over
come the financial benefits of graz
ing, and dairy graziers will have to
consider expanding their herd,
Noyes said.
To maintain a standard of living,
dairy farm profits must grow by 60
percent over 10 years. Even with
improved genetics, adoption of new
technology and increased efficiency,
the increase in net profit often can
not keep up with inflation.
"Unless dairy farmers can find
some way to increase profit per cow
every year, they will eventually need
to expand," Noyes said. "If dairy
producers adopted management
intensive grazing because they
think it will prevent their need to
expand, then they are mistaken."
Expanding a grazing operation
should be easier than expanding a
conventional dairy, if a grazier has
pasture space available, he said. A
grazing system requires less hous
ing, so adding cows can be done
inexpensively.
Spring is the best time for dairy
graziers to expand their herd
because that's when the most grass
is available in pastures.
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189