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Subject:
From:
Peter Borst <[log in to unmask]>
Reply To:
Informed Discussion of Beekeeping Issues and Bee Biology <[log in to unmask]>
Date:
Sun, 8 Apr 2007 21:04:22 -0400
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I looked over the paper and some key points seem to be:

Xiaolong Yang and Diana L. Cox-Foster: To our knowledge,
this is the first example of an ectoparasite immunosuppressing
its invertebrate host. Given that ticks immunosuppress
their vertebrate hosts, ectoparasites not only immunosuppress
their vertebrate hosts but also immunosuppress their
invertebrate hosts. Thus, immunosuppression of the hosts may
be a common phenomenon in the interaction and coevolution
between ectoparasites and their vertebrate and invertebrate
hosts.

We propose that varroa mites may cause collapse of honey bee
colonies as follows. Varroa mite infestation may reduce the
expression of genes encoding antimicrobial peptides and immunity-
related enzymes, eventually leading to depressed bee immunity
for both cellular and humoral immune responses. Thus,
the bee colonies may become more susceptible to various bee
pathogens, especially DWV [deformed wing virus].

* * *

Comment:
I have been wondering about the presence or absence of varroa at the time of
colony collapse. Some of the collapsing colonies reportedly do NOT have
heavy loads of mites. However, this neglects a key point: they may have had
them earlier, which could have caused a compromised immune system in the
colony, leading to eventual collapse -- even if the varroa were well reduced
by treatment or died off in some other way. Perhaps, the colony collapse is
less a factor of the *number* of the mites and more due to the virulence of
them or the pathogens they carry.

pb

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