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[SANET-MG] The Mysterious Disappearance of Honey Bees
 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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