>
> > How long can the DWV, Nosema C. and paralysis viruses stay in the hive
> even with a newly mated, non-infected queen?
We should first differentiate between the above three pathogens.
*Nosema ceranae* can be essentially "cleared," especially in late
summer--it is easy to find hives apparently free of infection. However,
due to its ease of being transmitted via floral visits, one can assume that
colonies are continually exposed to it.
The paralysis viruses tend also to self clear, since they tend to kill
infected bees quickly, and thus don't tend to go epidemic in a hive.
Some other viruses are more problematic, being nearly universally present
in colonies at all times, but kept in check by the bees' immune systems.
In rough order of concern they are:
DWV
BQCV
Lake Sinai Virus
Sacbrood virus
These are also transmitted via floral visits, and some (notably DWV) are
transmitted by varroa.
We're only learning recently about LSV, but it was linked to a batch of my
failing colonies in spring.
So long as a bee can hold DWV to about a million to a hundred million
(10\6-10\8) copies in its body, it is generally asymptomatic. But if that
bee is fed upon by an infected mite, the copy number can go much higher.
Once it passes around 10\11 copies, the bee's immune system fails
altogether, and that bee is toast.
There is currently not much that you can do directly about viruses, other
than to maintain varroa levels to not more than around 2 mites per 100
adult bees ALL SEASON LONG. Forget about higher "treatment
thresholds"--don't EVER allow mite levels to get much higher than that.
This will generally prevent an in-hive virus epidemic to gain a foothold.
As you fear, it takes a LONG time (weeks to months) for a colony to recover
from a DWV epidemic.
The second thing is to help the bees maintain their immunocompetence--which
is largely dependent upon optimal nutrition--provided by high-quality mixed
pollens or top-tier pollen subs.
--
Randy Oliver
Grass Valley, CA
www.ScientificBeekeeping.com
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