Getting the best from our bees
Saul Cunningham,
CSIRO Ecosystem Sciences, Canberra, ACT.
There has been growing interest
in bee pollination worldwide,
because it plays a significant role in
supporting food production. However
bee pollination is exposed to risks
from declines in honeybees and wild
bees. In Australia the pressing issue
is the risk that the Varroa mite, a
honeybee-specific parasite, will enter
the country causing serious problems
for beekeepers and at the same time
devastate feral honeybee populations
reducing the rate of free pollination.
This parasite has spread all around the
world so it is unlikely Australia will
remain Varroa free in the long run.
We know much less about whether
Australian native bees are vulnerable
to environmental change, although
studies elsewhere in the world have
shown that native species have
suffered because of habitat loss and
other pressures.
The two major nut crops grown in
Australia, almonds and macadamias,
benefit greatly from bee pollination.
In fact, the pollination requirement
for almonds is so great that almond
growers are the single largest
purchasers of honeybee pollination
services in Australia, drawing in hives
from all over the country. Because the
almond industry is still expanding, the
demand for hives will grow for years
to come. If a major honeybee disease,
Almonds share with macadamias, a high dependency on pollination
for good yield, (Photo: ABA)
such as Varroa, were to establish in
Australia this would directly impact
the almond industry. Impacts could
include a shortage of hives, increased
cost per hive, or quarantine barriers to
hive movement. With this background
a research project was developed by
the Almond Board of Australia and
Horticulture Australia Limited with
CSIRO and Australian Beekeeping
Services. The over-arching goal is
to determine how many bees are
necessary to support good nut yield.
The project examines if there are
pollination strategies that can help
Wild pollination is known to play a bigger role for macadamias than for almonds.
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growers maintain or even increase
the nut crop, and asks is it possible to
maintain high yield with fewer hives,
or does yield maximisation demand
even more hives than are currently in
use?
While it is simple enough to
ask “what happens if we use fewer
hives?”, there are many challenges
to conducting a full-scale field
experiment. Of course, experimenting
with lower bee numbers could lead to
a lower nut crop – so this experiment
required the generous co-operation
of growers, willing to share the risk
in the interest of science. In the 2011
flowering season we conducted “low
pollination trials” in 6 almonds blocks
in the region around Renmark, South
Australia.
The second challenge was to
actually reduce the number of bees
in the orchard. Our strategy was to
work in an area where the standard
commercial pollination hives were
excluded, and in which we provided
only a small number of hives. After
a lot of observation over thousands
of flowers and many hours, our data
showed that we did create “low spots”
and “high spots” for honeybee visits
but, most importantly, the low spots
for visitation were not necessarily low
spots for nut set.
This first year of data has given
us the confidence to know that while
AUSTRALIAN NUTGROWER
JUNE 2012
honeybee visits are undeniably
essential to a good nut crop, there is
not always a tight relationship between
number of bees and amount of nut set.
Indeed it might be that we often have
more bees than necessary for good
fruit set. Maybe we can use fewer bees
without lowering the yield?
There are some critical issues
to sort out before we could suggest
that lowering bee numbers is a safe
strategy. One is with regards the
weather. Honeybees are less active in
cold or rainy weather, so high numbers
of hives in the orchard are sometimes
seen as an insurance against a cold
or wet flowering season. In other
words, ”lets use more hives to make
up for the risk that each hive might
be a bit less efficient”. This kind of
risk management is important for us
to build into any future pollination
strategies.
It is interesting to note, however,
that an analysis of 23 years of weather
and almond yield data in California
found no evidence that cold or wet
flowering seasons led to lower yield,
so the weather problem for bee flight
may be less important than expected.
The second major issue is that our
first year experiment only achieved
a relatively small lowering of bee
numbers and we need to know more
about what will happen if bee numbers
are even lower. In the 2012 flowering
season, our research goal is to observe
flowers on more trees that are further
away from hives, to learn more about
what happens at these locations with
even fewer bees. We know enough
about almond pollination to be certain
that if you get low enough bee numbers,
there will be a negative impact on nut
set, but we don’t really know how low
this threshold is, in terms of bee visits
per flower, or hives per hectare.
What about those wild bees? There
is strong evidence worldwide that
wild bees often provide a high level of
service for crops. In some studies we
see that the abundance and diversity
of wild bees is a better predictor of
fruit success than is the abundance of
the domestic honeybee. The problem
is that in large scale orchards there is
usually not enough pollinator habitat
to maintain enough wild bees. Recent
research in California showed that
wild bees were effective for almond
pollination, but only in locations
where bee nesting habitat was not too
One of the main outputs of the research will be a better understanding of what
the best number of hives per hectare will be in Australian almond orchards.
(Photo: S. Cunningham)
far away. So, there is a real benefit
to agriculture coming from nearby
non-agricultural land, but where
orchards are large and pollination
demand is high, wild pollination
must be supplemented with managed
honeybees. Almond orchards in
Australia typify this large-scale, high
demand situation.
One of the main outputs of the
research will be a better understanding
of what the best number of hives per
hectare will be in Australian almond
orchards. But watching the bees, I
can’t help but get frustrated, and think
“if only we could use fewer bees, but
make them work smarter!” The trouble
is that the great majority of visits
involve bees going from flower to
flower in the same tree, or sometimes
to the next tree in the row. Most of
this activity is making no difference at
all to pollination, because pollination
only occurs when pollen is transferred
between varieties, which are planted
in adjacent rows. We know that if
we could increase the frequency with
which bees move between varieties
we would achieve much greater
pollination efficiency, but how can this
be done?
There are no easy solutions here,
but we will examine the potential of
some techniques which can affect
bee behaviour. For example, a device
on the hive can remove pollen from
bees, encouraging them to spend even
more time pollen-foraging, perhaps
helping cross pollination. We will
also examine the impact of putting
“bouquets” of flowers from a crosspollinating variety into the canopy
of compatible trees. This will surely
increase cross-pollen transfer, but we
do not know how big the effect will be,
or over what distance it will occur.
We are only one year into a three
year project, so there will be plenty
more to learn. The work will provide
many more insights into pollination
of almonds by honeybees, and these
in turn will help improve pollination
strategies, and provide confidence
that we have a good knowledge base
for managing the overall commercial
pollination requirements of the
industry. Beyond this, many of the
challenges for almonds are similar
to those for other orchard crops, and
we are interested in making sure the
knowledge is shared.
Which brings us back to
macadamias. They share, with almonds,
a high dependency on pollination for
good yield, but are of course grown
in a very different environment. In
particular, wild pollination is known to
play a bigger role for macadamias than
for almonds. There is great potential to
adapt some of what we are learning
for almonds, but also to examine the
special circumstances for this crop and
to make sure this industry also has the
best possible pollination outcomes.
N.B. Saul Cunningham will be
presenting the 2012 pollination season
trial results at the Almond Conference
to be held 8th-10th October.
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