OIE news Causes of bee colony mortality Reza Shahrouzi International beekeeping consultant,
The environment and agriculture depend on a wide variety of pollinating species, including 20,000 species of hymenoptera,
P.O. Box 34185-451, Qazvin-Iran.
the most important being the domestic honey bee (Apis mellifera).
E-mail:
[email protected]
Worldwide, the annual value of this ecological service is estimated to be in excess of a hundred billion dollars. Since 1997, numerous eye-witness accounts and published articles have reported an apparent weakening and mortality of bee colonies in various countries around the world. The beekeeping profession estimates that national production of honey fell by 20 to 30% between 1997 and 2009. The depopulation observed in apiaries is sometimes severe, leading to a reduction in honey production in the same proportion as the reduction in the number of bees. The weakening that occurs at the end of the beekeeping year may also result in a higher frequency of mortalities in winter.
One can define six categories of causes of mortality of bee colonies: – bee diseases and parasites; – chemical products; – the environment; – beekeeping practices; – agricultural practices; – treatment of varroosis.
Bee diseases and parasites
mortality of bee colonies, some have been highlighted in the most recent
Like all living organisms, bees may be
The pathogens responsible for diseases
investigations into the phenomenon
exposed to a variety of chemical
and parasitic infestations are predators:
of weakening, collapse and mortality
substances potentially present in the
parasites, fungi, bacteria and viruses.
of bee colonies, either individually
environment. In crop producing areas,
or in association with others. This is
most of these chemical substances
pathogens of bees. This precise figure
the case with Varroa destructor,
come under the heading of
is based on numerous bibliographic
alone or in association with other
phytosanitary products or pesticides.
references, including recent studies on
biological pathogens (viruses;
A phytopharmaceutical product is any
the decline of bee populations. While all
Tropilaelaps mercedesae and
product that, through its mode of
of them have the potential to cause
Nosema ceranae).
action, is designed to protect a crop
To date, there are 29 known
Chemical products
2009 • 4
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all the vital functions, such as enzymatic functions and reproduction. Pollen is notably involved in the development of the hypopharyngeal glands of young bees and their fat body. If the pollen intake is insufficient these glands do not develop correctly in nurse bees, whose production of royal jelly no longer allows normal development of the brood or adequate food for the queen (the protein supplied by hypopharyngeal secretions represents about 95% of the protein required for the development of a larva). Pollen is stored in cells in the form of bee bread, comparable to silage, and has a higher biological © LeConte Pollen-gathering bee on acacia
value than fresh pollen due to fermentation (through the action of
from a harmful organism and usually
thermoregulation, various tasks
three strains of Saccharomyces and a
has a specific action for a given type
involved in maintaining the hive such
strain of lactobacilli) (Pain & Maugenet,
of target. Such products include
as cleaning cells, feeding the brood,
1966). Since the protein content varies
fungicides, herbicides, insecticides,
foraging, etc. Carbohydrates are usually
according to the botanical source, the
nematocides, molluscicides,
stored in the body as fat. The sugars
required amount of pollen to supply
rodenticides and avicides. The
present in floral secretions (nectar) are
a given quality of protein can therefore
catalogue of phytosanitary products lists
metabolised by bees (glucose, fructose,
be 50% less if the protein level
some 450 active agents and some
trehalose, maltose), whereas those
increases from 20% to 30%. In a
5,000 corresponding commercial
present in the secretion (honeydew)
period of medium honey flow, this level
products (survey conducted by the
of certain insects are not (raffinose).
must be at least 25%, and exceeds
French association ACTA (Association
Thermoregulation is a very important
30% during periods of heavy honey
de coordination technique agricole).
requirement, in particular to maintain
flow (Kleinschmidt, 1986). The
a temperature of 34°C in the presence
balance between amino acids varies
of brood.
considerably according to the plant
The environment
source. Very little information is currently
The environment is frequently
swarm should not fall below 13°C. In
mentioned as a potential cause of
temperate regions, a bee colony’s sugar
available on the nutritional
mortality of bee colonies: two factors
consumption can range from 19 to
requirements of bees in terms of lipids
that have been incriminated are food
25 kg in winter and total around 80 kg
(fatty acids, sterols and phospholipids).
resources and climatic factors.
during a full year. Numerous factors
These requirements are provided for
affect the quantity and quality of pollen
by the consumption of pollen. Of the
and nectar gathering by an apiary.
lipids, sterols are involved in the
Food resources Carbohydrates are among the most
6
In winter, the temperature of the
Protein is provided by pollen.
production of the moulting hormone
important food constituents, covering
A sufficient intake is essential for a bee
(ecdysone) and are therefore
the energy requirements for
colony, to ensure growth and maintain
indispensable.
2009 • 4
OIE news same as those normally found during
queen can result in the death of the
do not appear to pose such serious
the brood period (1.5% CO2 and 35°C
colony if it occurs during the period
problems as protein, carbohydrates or
within the hive), the physiology of the
when there are no males and
water requirements (Bruneau, 2006).
bees corresponded to that of summer
consequently no insemination.
Mineral and vitamin requirements
bees, with a very short lifespan. When
Whenever the colony is visited, every
adequate supply of water can be a
It should be emphasised that an
the CO2 concentration was held steady
care must be taken not to disturb the
serious problem, especially during
but the temperature was lowered from
queen. Beekeepers must also keep
periods of heat wave, since the decline
35°C to 27°C, worker bees became
a check on the age of queens by
in the availability of water can be an
physiologically similar to winter worker
marking them. Regular renewal
important limiting factor for the survival
bees (Bühler et al., 1983).
of queens will help to maintain optimal
of colonies.
Crailsheim et al. demonstrated that
vitality, which is usually limited to
climate disturbances affect the
the first two years of their life. Colonies
Climatic factors
behaviour of nurse bees and foraging
should not be divided too late in
After a period of excessive drought,
bees, in particular with regard to
the year, so as to reduce the risk
the flowering of melliferous and
collection of nectar for the hive and
of the new colonies being insufficiently
polleniferous plants can rapidly die
food distribution within the hive.
developed in winter.
down during the summer and stop
Climatic conditions can therefore
completely. Low temperatures and
influence the development of the colony
important. To encourage colonies
especially sudden cold spells affect
and lifespan of the bees (Crailsheim
to thrive, commonsense rules must
the development of bee colonies.
et al., 1999).
apply: humidity should be kept as low
General apiary maintenance is also
Temperature is a determining factor
as possible within the hives, the
for the vitality of a colony; bees
beekeeper must insulate the hives from
maintain the brood temperature at
Beekeeping practices
the ground and ensure that rainwater
34.5 ± 0.5°C, regardless of fluctuations
It is essential for colonies to maintain
does not accumulate; the apiary must
in the ambient temperature. If,
a balanced population, given the
be kept clear of vegetation and the
however, the brood temperature is
complex organisation and working
supports used for the hives should not
raised, the emerging bees, though
relationships between their individual
retain water; the flight path must be
morphologically normal in appearance,
members. A shortage of workers, nurse
kept free from obstruction and a
present impaired learning and
bees or foraging bees can lead to
source of drinking water must be
memorisation (Tautz et al., 2003; Jones
disturbances within colonies. During
provided near the apiary.
et al., 2005). Bühler et al. studied the
beekeeping procedures a demographic
effects of CO2 concentrations and
balance must be maintained. The
spring and early summer to prevent
temperature on bees within the hive:
beekeeper’s role is to use the
or halt swarming wherever possible.
when climatic conditions were the
appropriate techniques and methods to
During swarming, nearly half – and
promote the sustainability of colonies so
sometimes as many as two-thirds –
as to ensure their annual production of
of the population leave the hive to start
honey. A lack of workers and therefore
a new colony.
Regular visits should be made in
This phenomenon may be triggered
of nutritional resources will lead to a slower development of the colonies and
by the temporary absence of a fertile
an insufficient population. If there are
queen. Visiting the colonies provides
not enough bees during the winter
the opportunity, where necessary, to:
period, they will be unable to maintain
–
the necessary temperature to ensure
underway: increasing the volume of the
the survival of the swarm. Loss of the
hive, creating artificial swarms, etc.;
prevent swarming from getting
2009 • 4
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OIE news –
avoid swarming due to the
destruction of royal cells; –
determine the cause of colony
population decline. In temperate regions, swarming may occur up to the end of June and it may take several weeks for the colony’s population to return to normal. In addition to the fall in the number
© LeConte Pollen-gathering bee on lavander
of bees, there is also a considerable drop in honey production. Moreover,
Indeed, after collecting the honey and
These selection criteria were used
after swarming has taken place the
therefore the reserves of carbohydrate
to the detriment of the criterion of the
beekeeper must adapt the volume of
stored in the supers, the beekeeper
hygienic behaviour of bees to one
the hive to the remaining population
must provide the bees with a
another and to the brood, the latter
to minimise any unnecessary
substitute, since lack of food will lead
having been far less taken into account
expenditure of energy and avoid the
to the death of the colony. Four
than the previous two criteria.
development of parasites, and
different situations can give rise to
especially wax moths, in empty spaces.
starvation:
apiculture is related to the way
The life cycle of a colony,
–
an insufficient quantity of food;
beekeepers use products to control the
and indeed its survival, are highly
–
beekeeping methods (provision of
various pathogens that can develop in
dependent on the vegetation in the
food) unsuited to the needs of a new
their apiaries. For a number of years,
environment and more specifically
strain of bees;
phenomena of resistance to acaricides
on the available sources of pollen
–
have appeared in a number of
and nectar. Two factors must be taken
lasting into spring, and preventing food
countries, reducing the effectiveness of
into account when setting up an apiary:
collection;
the molecules approved for use against
– the nutritional resources available
–
V. destructor. This resistance
throughout the season and more
alternation of short warm spells and
phenomenon is thought to be largely
especially before the critical winter
longer periods of cold weather, leading
due to the application of a control
period;
to the opening and closing of the
strategy based on the use of a very
– the number of colonies per apiary.
swarm of bees, some way from the still
small number of acaricidal molecules in
abundant food stored in the hive
apiaries, without any alternation in their
(Haubruge et al., 2006).
use. Resistance to fluvalinate and other
A large number of colonies per site can be considered during the flowering
climatic conditions with the
The selection of queens can be a
of highly melliferous and polleniferous
acaricides has been described in many
plants. However, when food becomes
risk factor related to beekeeping
countries and could have major
scarcer the number of colonies per site
practices.
consequences for treatment efficacy
Current selection criteria are
must be adapted so that each of them
(Elzen et al., 1998; Pettis, 2004;
will have sufficient reserves of proteins
considered to be inadequate to ensure
Faucon, 2000; Shahrouzi, 2007). Thus,
and nutrients for the development of
healthy, strong and productive colonies
it could be insufficient for beekeepers
the longer-living winter bees.
(Imdorf et al., 2007). Up to now,
to apply a single treatment against
selection has always been based on:
mites in autumn, since the damage
installed in colonies, this can lead to
–
inflicted on the population of the colony
food deficiency and poor requeening.
specifically the absence of
When pollen traps are permanently
Another proven cause of mortality is a lack of food during the winter period.
8
unfavourable climatic conditions,
Another factor arising from
2009 • 4
the behaviour, and more
aggressiveness, of bee colonies; –
honey productivity.
could already be too great. Beekeepers may contaminate apiaries by:
OIE news –
resources for honey bees. The decline
However, experience has shown
healthy hives, brood or bees from
introducing bees (introduction of
in the biodiversity of polleniferous and
that, whatever the treatment, a small
affected or contaminated colonies);
melliferous plants in agricultural
but variable number of colonies will
–
environments is the direct consequence
retain a high level of parasitism and
colonies that have been cured but are
of a combination of two factors: the use
thus be a source of contamination and
still carrying other pathogens;
of herbicides, whether non-selective or
weakening for other colonies in the
–
selective, and single-crop farming,
apiary.
combining healthy colonies with
reusing hives without prior
disinfection.
especially when it involves crops such
Of the medicinal products that have
as cereals that are of no value to bees.
received marketing authorisation,
Fields of phacelia or white clover and
Apivar NT and Bayvarol® currently
sainfoin are very often visited by
have a sufficient level of efficacy and
There have been considerable changes
foraging bees but are often mown
should therefore be given priority.
in agricultural practices during the last
before the end of flowering, resulting in
few decades.
a considerable loss of bees through
Agricultural practices
In the majority of production areas,
lack of food.
crop management has been simplified,
Colony collapse disorder (CCD) has
leading to a scarcity of some melliferous plant species and especially leguminous plants.
Colony collapse disorder been described as a syndrome
Treatment of varroosis
involving a rapid decline in a colony’s
The first treatment must be carried out
adult bee population without any dead
in late September or early October to
bees being found in or around the
these areas, to the detriment of insect-
give overwintering bees the optimum
colony (Oldroyd, 2007; Stokstad,
pollinated species (rape, field beans,
potential for survival. It must be
2007a, 2007b). In the terminal phase,
clover, etc.). It is important to
sufficiently effective to ensure that at
the queen is reported to be no longer
emphasise the damaging effects of
the end of the treatment there will be
surrounded by more than a few newly
single-crop farming, which tends to
fewer than 50 parasites within treated
emerged bees despite the fact that the
result in an alternation of over-supply
hives. Effective treatment applied at the
hive still contains reserves of food and
and shortages and is also based on
appropriate time is of prime
capped brood cells. The CCD
plants that are poor in pollen and
importance. There are several risk
phenomenon has principally been
nectar (e.g. cereals and sunflower).
factors in addition to the parasite
observed during winter losses and the
Furthermore, there is also a destructive
burden, such as the nutritional quality
bees analysed are those that have
management of the fixed features of
of the bees’ supply of pollen in autumn
survived (CCD having caused the
the landscape, such as embankments,
(for the development of fat), the
disappearance of the majority of the
hedges, roadside verges, and grassland
presence of opportunistic parasites
colony’s population). Some authors
alongside rivers and communication
such as Nosema sp., the beekeeping
have emphasised the no doubt
routes. Intensive agricultural practices
environment (degree of contamination
important role of V. destructor in this
thus result in a decline in food
from infested apiaries in the
phenomenon. The initial studies on
surrounding area), the severity of the
CCD had revealed the presence of
coming winter, etc.
numerous pathogens without being
Cereal crops often predominate in
© LeConte Pollen-gathering bee on heather
If an apiary’s colonies are located in
able to pinpoint any one specific cause
an area conducive to the early rearing
for the phenomenon (Pettis et al.,
of brood (potential source of
2007). Nevertheless, preliminary
development for the parasite), the
observations tend to show that CCD is
second treatment must be carried out
transmissible and therefore potentially
in early spring.
due to one or more pathogens.
2009 • 4
9
OIE news
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OIE news Shahrouzi R. (2008). – L’apiculture dans le développement agricole l’exemple de la région de Rustaq en Afghanistan (www.beekeeping. com/articles/fr/apiculture_developpement_agricole _afghanistan.pdf). Shahrouzi R. (2008). – Natural and chemical
new OIE publications
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Lengua azul en el norte de Europa (Bluetongue in northern Europe)
Spanish version just printed
Science, 317 (5843), 1304-1305. Stokstad E. (2007b). – The case of the empty hives. Science, 316 (5827), 970-972. Tautz J., Maier S., Groh C., Rossler W. & Brockmann A. (2003). – Behavioral performance in
Coordinated by C. Saegerman, F. Reviriego-Gordejo & P.-P. Pastoret In Spanish
adult honey bees is influenced by the temperature
Format: 16 ⫻ 24 cm
experienced during their larval development. Proc.
96 pp.
Natl. Acad. Sci. USA, 100, (12), 7343-7347. Vanengelsdorp D., Underwood R., Caron D. &
ISBN 978-92-9044-725-2 Price: € 35
Bluetongue (BT) is an infectious, viral and vector-borne disease
Hayes J. (2007). – An estimate of managed colony
of improved breeds of sheep and
losses in the winter of 2006-2007: a report
some species of deer that is of major
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international importance. The infection
American Bee Journal, 147 (7), 599-609.
is usually unapparent in cattle, which acts as reservoir for the virus. However, some serotypes such as serotype 8 (BTV-8), which recently caused a severe epizootic of BT in northern Europe, exhibit a more important virulence in cattle. Consequently, the redaction of a scientific booklet describing Bluetongue is of great utility for veterinarians and animal health professionals in the framework of an early detection of Bluetongue and other emerging diseases.
2009 • 4
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