Greetings

It seems quite obvious that to control the collapse of honey bee colonies,
you have to control the viruses. This means getting rid of the mites which
carry & transmit the virus. Although honey bee colonies vary on the number
of mites that will kill them, having large numbers of parasitic mites would
be harmful even without the viruses.

* * *

In the first five years after V. destructor was detected in Britain SPV
infections appeared in severely infested colonies, whilst towards the end of
that period DWV began to be detected. In the second five-year period, SPV
continued to increase in prevalence, and DWV became almost universal. 

The markedly greater prevalence of SPV in experimental colonies in
comparison to the national average in infested colonies may be explained by
the absence of mite control measures in these colonies and the natural
spread of mites containing virus to neighbouring colonies also used in studies.

 – VIRUS SUCCESSION IN HONEYBEE COLONIES INFESTED WITH VARROA DESTRUCTOR. 
N.L. CARRECK, et al

* * *

If you have found several of your hives dead or moribund, for no apparent
reason, you are not alone. Often, there are hardly any dead bees, never mind
live ones. Norman Carrick, from Rothamstead, said it was almost certainly
due to virus infection, probably vectored by varroa. Paralysis virus or
deformed wing virus are the most likely culprits. 

In the latter, the bees can be infected as adults as well as larvae, which
greatly shortens their life span. If the autumn bees are infected they
simply do not live long enough to get through the winter, but crawl out to
die, or are cleaned out by healthy bees. Hopefully, any remnants that have
survived so far will pick up as the weather improves.  

-- THE APIARIST May 2005

* * *

Autumn is the time at which the colony is at greatest risk to viruses and
maintaining a mite population below 2500 will prevent APV epidemics and
confine DWV to low levels. To prevent DWV epidemics would require treatment
at smaller mite populations, i.e. reducing the mite population to below 700.
If prevention of DWV is an aim then this may be more easily achieved at the
start of the summer when the threshold mite load required to eliminate DWV
is larger. 

It is, however, difficult to eliminate completely any bee virus from a
colony, since the reduction of the mite population does not affect the
normal cycle of bee to bee transmissions that allows the virus to persist at
inapparent levels within the colony. Sporadic appearance of overtly infected
bees will always occur and if sufficient mites are present the viral-mite
transmission route will become re-established. 

-- The dynamics of virus epidemics in Varroa -infested honey bee colonies.
D. J. T. SUMPTER, et al

* * *

Because most if not all infested EHB (European Honey Bee) colonies are
unable to prevent the relentless growth of the mite population they all
eventually die. The timing of colony collapse is dependant on the presence
of overt infections of key bee viruses such as DWV, slow and acute paralysis
viruses. Under temperate conditions in autumn, when the colony is at most
risk, a mite population of 700 mites is needed to sustain a DWV infection
within a typical colony, while 3000- 4000 mites are needed to actually cause
the death of the colony. 

However, under sub-tropical/tropical conditions where brood is almost
continuously reared then over 2000 mites are needed to sustain the
infection, while 6000-12000 mites (depending on the size of the colony) are
needed to kill it. 

However, this increase in mite threshold level under subtropical/ tropical
conditions is more than offset by the mite's better growth potential under
these conditions. This explains why all infested EHB colonies collapse as
they are unable to prevent either the mite population growth or appearance
of the viral pathogens 

Peter Borst
NY State
USA
-- INTERACTIONS BETWEEN HONEYBEES, BEE VIRUSES AND VARROA  Stephen J. Martín 

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