[permaculture] The Mysterious Disappearance of Honey Bees

Lawrence F. London, Jr. lfl at intrex.net
Mon Mar 5 12:29:11 EST 2007


-------- Original Message --------
Subject: [SANET-MG] The Mysterious Disappearance of Honey Bees
Date: Mon, 5 Mar 2007 08:20:30 -0500
From: jcummins <jcummins at UWO.CA>
To: SANET-MG at LISTS.IFAS.UFL.EDU

Prof. Joe Cummins
The Mysterious Disappearance of Honey Bees
In October 2006 United States National Research Council published the
report of their Committee on the Status of Pollinators in North America,
The report pointed out that an existing decline in honey bee pollinators
was devastating North America. The report pointed out the importance of
pollinators noting that three quarters of the earth’s flowering plants
depended on pollinators for propagation. The extensive report dealt with
bureaucratic issues aimed at dealing with the catastrophe and delineated
ways that more human and financial resources should be focused on honey
bee decline The report did not pin down causes in decline but instead
focused on introduced parasites and microbial disease causing organisms
such as fungi, bacteria and viruses Other causes included habitat
decline, fragmentation and deterioration. The remedies suggested
included testing commercial pollinators to insure that they were disease
free and similar bureaucratic measures rather than a sharp focus on the
primary causes of decline (1). The impact of pesticide on bees the uses
and the spread of genetically modified (GM) crops modified for insect
resistance and herbicide tolerance were barely discussed in the report
leaving the impression that these were not considered important by the
committee. The following discussion will deal with those important
issues regardless of the views of the NRC Committee.
Science Magazine reported on the pollination crisis but emphasized the
need to replace the current pollinators with more robust insects (2).
The New York Times emphasized the impact of bee decline on farmers and
reported a salient observation that bees were flying off from the hive
and simply not returning.(3). The Independent commented on the swift
colony decline and noted that the problem of a tremendous pathogen load
in the remaining members of a colony (4). The cogent point is that the
bees in the colonies appear to have lost their immunity to viruses,
bacteria and fungal diseases. The loss of resistance to disease may be
caused by parasites, virus infections, or pesticides (both applied and
present in GM crops).The disappearance of bees may have originated with
one thing that diminished the bee’s immunity or by a combination of
environmental factors diminishing the immune system ,all hitting the bee
colonies at the same time.
Parasites reduce bee immunity : Varroa mites (Varroa destructor) were
fist observed in the United States in the mid 1980s , they appear to
have jumped from native bees to honey bees in the Orient during the mid
1960s. The parasite was first observed in North America in the mid
1980s, since that time they have spread throughout North America. The
parasite invades the hives and sucks the hemolympth from the pupae and
adult bees infecting them with viruses carried by the parasite. The
parasite reduces the immune response of the bees causing them to be
prone to infection with virus, bacteria or fungi (5,6). A number of
virus diseases are enhanced in the parasite infected bee colony ,
particularly the deformed wing virus disease that causes crippling
deformity in the bees (7). Multiple viruses frequently infect the bees
attacked by Varroa parasite. These viruses are spread no only by the
parasite but vertically from queen to brood (8,9). The parasite infected
colonies are frequently treated with a pyrethroid insecticide ,
fluvalinate, but this insecticide may influence the behaviour of the
honey bee and has well the parasite has grown resistant to the
insecticide (10). Honey bee disappearance has not always been associated
with parasite infection and it is clear that man made environmental
contaminants may influence bee immunity and bee behaviour. The immune
pathways of bees have been studied. Honey bees have 17 gene families
involved in immunity but they have roughly one third the number of genes
involved in immunity as have Drosophila and Anapheles Mosquitoes. Honey
bees seem to have limited immune flexibility (11). The immune
inflexibility of honey bees may make them sensitive to devastating
pathogens.
Pesticides may have sublethal effects on bees: Most of the information
on pesticides reports the lethal effects on insects or on non-target
beneficial organisms. Bees are particularly sensitive to pesticides,
whether insecticides, fungicides or herbicides, that effect development,
adult longevity, immunity or behavioural effects such as navigation,
feeding behaviour, oviposition, or learning. Sublethal effects can prove
fatally disruptive to hive communities. Numerous pesticides have been
found to disrupt bees following sublethal exposures (12). A wide array
of pesticides including insecticides and fungicides including
fluvalinate (the chemical used to treat hives to eliminate parasites)
disrupted the behaviour of honey bees leading to feeding and navigation
problems (13). Bees suffering from sublethal pesticide intoxication
resembled the behaviour of bees described by observers of honey bee
disappearance phenomenon. Sublethal doses of fipronil (a veterinary
insecticide) in honey bee impaired the olfactory memory process (14).
Spinosad, a prominent and much used natural insecticide fed to bumble
bees in pollen were slower foragers while a higher dose of the
insecticide caused colony death within two to four weeks (15). It is
difficult to find studies on the impact of herbicides on bee behaviour
and such studies are desirable. A study of the effect of glufosinate ( a
glutamine synthesis inhibitor) on the bees gut microbes showed that over
half of the gut microbes were sensitive to the herbicide (16).
Glufosinate had pronounced insecticidal activity towards the
caterpillars of skipper butterfly (17) Glutamine is important in sensory
nerve transmission in insects.
Genetically Modified (GM) crops may have sublethal effects on bees: The
possibility that the great distribution of GM crops in North America is
contributing to the decline in honey bees was given little consideration
by the NRC Committee studying the problem (1) even though the time that
the decline appeared was at the time GM crops were first widely
deployed. GM crops are either modified to tolerate herbicides including
gyphosate or glufosinate or to contain insecticides (the Bt Cry toxins).
The insect resistance toxins produced in GM crops are not highly toxic
to bees they are toxic to moths and beattles but in some instances the
toxins cause bee lethality or behavioural modification. The Bacillus
thuringiensis (Bt) toxin Cry1Ab caused reduced foraging activity before
and after treatment with syrup containing the toxin. However,the Bt
toxin produced less pronounced impacts on bee behaviour than did the
chemical pesticides deltamethrin or imidacloprid (18). Bt bacteria
caused mortality in bees when fed in broth cultures or sugar solutions
(19). A number of purified Bt Cry toxins have been studied in the
laboratory to determine their toxicity to honey bees and bumble bees.
For the most part, those studies showed little threat from the Cry
toxins. However, sublethal effects on the bees were not recorded in the
experiments (20). Transgenic glyphosate resistant canola pollen posed no
threat to honey bees (21). Organic, conventional and herbicide resistant
Canola were compared regarding the pollination by wild bees in Alberta,
Canada. The herbicide tolerant canola plots had the greatest pollination
deficit , while conventional and organic plots were equally well served
by the wild bees (22). Fuller studies are needed to evaluate the impact
of GM crops on sublethal effects such as learning and feeding behaviour.
The potential consequences of pollinator declines on stability of food
crops and on the conservation of biodiversity has been discussed. The
loss in food production can be staggering and the impact on biodiversity
may be irreversible(23).
In conclusion, the decline in honey bees is likely to be far from
finished. The most significant factor in this decline may be fundamental
it may be the well documented inflexibility in the genes of the bee’s
immune system. Immune inflexibility was not discussed in the NRC report
on bee decline (1). That factor is , most likely, the primary hurdle in
an ultimate reversal of the decline. Using genetic techniques such as
microarray analysis and marker assisted selection it should be possible
to create honey bees with robust immune systems. In the absence of such
robust honey bees it is clear that honey bees cannot be treated like
“babies in a bubble” to protect them from toxins and pathogens in the
environment. Agents impacting on the honey bee immune system go beyond
mites to chemical pesticides and to some degree GM crops. Bees need to
be protected from the agents that interfere with their immunity or
behaviour. However, the NRC Committee report (1) does little to
establish a broadly based approach to identify and control the
pesticides and crops causing the decline. The NRC report is narrowly
focused and should not be considered a serious effort to deal with the
decline of honey bees. The impact of pesticides and GM crops requires
fuller attention as does a program to create honey bees with robust
immune systems.
References




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