On Sat, 6 Oct 2007 17:45:42 +1000, queenbee <[log in to unmask]> wrote:
>As I recall Tibor Szabo did some work when he was at Beaverlodge on dusting
>with fumagillin.  Does anyone else recall this or is my memory in need of a
>good defrag?

NOTE: Most of this is scavenged from an article I wrote (one of my better
ones)... the dusting is addressed right off the bat... 

Nothing wrong with your hard drive Trevor.  Oddly in the March 1987 issue of
American Bee Journal two articles appeared regarding the efficacy of feeding
fumagillin in a dusting powder in the spring.  One study was conducted in
British Columbia’s mild Lower Mainland (Wyborn and McCutcheon) and the other
was the one you remembered from Beaverlodge, Alberta (Szabo and Heikel).  In
both studies colonies were medicated with 200 mg of fumagillin in syrup the
previous fall (slightly above the label rate on Fumagilin-B) and, yet,
nosema had become detectable by the spring.  Colonies were evaluated for
nosema levels in the beginning of March and in Langley each bee had
approximately 360,000 spores and in Beaverlodge the count was 15 million.  

The colonies in Langley were either left untreated or treated with a total
of 300 mg fumagillin applied weekly over three weeks, beginning on March
14th.  The same dose of fumagillin was either applied in powdered sugar or
in syrup.  The nosema levels among untreated colonies shot up and by April
12th levels had reached 1.6 million spores per bee, a four-fold increase. 
By contrast, both methods of administering fumagillin, either in syrup or
dust, resulted in nosema levels below 100,000 spores per bee.  Clearly, dust
was as effective as syrup.

The research in Beaverlodge came to a similar conclusion.  Their experiment
involved either leaving colonies untreated or treating them with a total of
58.8 mg of fumagillin in powdered sugar applied on April 4th and April 14th.
 Three weeks after the second treatment, treated colonies had 4.5 times
fewer spores per bee.  Although fewer spores were found the treated colonies
were left with a fairly high number of spores (4.8 million).  It is
important to remember, however, the dose used in the Beaverlodge study was
five times lower than the study in Langley and initial nosema level in
Beaverlodge 40 times higher.  As the authors of the Beaverlodge study
speculated “perhaps an application of 100 mg fumagillin in icing sugar
during early spring would eliminate Nosema disease”.  

Think, however, what it would cost to treat with 200 mg in the fall and 200
mg in the spring?  It would mean ~$2.50 per colony per treatment, thus
~$5.00 per colony.  Whew.  That's a lot.

Springtime management would be easier to direct if it was possible to know
which bee yards had nosema.  Unfortunately, sensitive detection of nosema is
only possible by looking for the microscopic spores from crushed bee guts. 
Not guts exactly, but specifically the part of the gut to the rear of the
honey sac called the ventriculus (to the rear of the honey sac, but in front
of the big brown rectum).  Although the white soft and swollen ventriculus
of infected bees is easily distinguished from the straw brown color of
healthy bees, this symptom is not reliable unless bees are heavily infected
- I have run cages of bees inoculated with nosema and often bees with
seemingly normal guts are full of nosema.  Microscopic analysis is essential.

Where should be samples be taken from a colony and what do they mean? 
Swedish research by Ingemar Fries and his colleagues sheds some light on
these two questions.  Their research involved careful analysis of bee
samples collected from several dozen colonies in the early spring followed
by measurements of the total summer honey crop.  The research tied summer
honey production to spring nosema levels to determine what level of nosema
would reduce beekeeper honey revenues.  Each colony had samples of 60 bees
taken from either the bottom board (dead) or from the cluster (live).  The
live bees were then analysed for the number of infected bees in the sample
OR the number of spores in a pooled sample of bees.  

The important results of the research were that: 1) live adult bees taken
from the cluster are more predictive of than dead bees from the bottom board
and 2) the number of infected bees in a sample is more predictive than the
total number of spores in a composite sample.  The researchers determined
that summer honey yield was reduced by half if pooled samples had
approximately 15 million spores per bee or 48% of the bees in the sample had
nosema.  

Clearly the prospect of testing each of your colonies for nosema is
daunting, and probably not economically viable.  Nonetheless, the finding
leaves the door open for new research to evaluate different schemes to
sample of a more realistic management unit, perhaps a bee yard, to determine
if treatment is necessary.  

Spring comb replacement is another area which appears to hold promise for
managing nosema.  Dr. Fries investigated the benefit of replacing all brood
comb with foundation early each summer for five consecutive years.  Each May
the levels of spores in a group of unmanipulated colonies was compared to
colonies in which the brood comb was replaced.  Over the five years, comb
replacement resulted in a 30% drop in the number of colonies with detectable
nosema levels each spring.  The replacement of comb did not influence honey
yield and the five year average production was 173 pounds.

I do not expect many beekeepers will go out and replace their entire
inventory of brood comb this spring, however the study is useful in pointing
out the importance of implementing routine brood comb replacement. 
Furthermore, irradiation and fumigation with 60% acetic acid have been shown
to kill nosema spores on unoccupied comb and both techniques may help reduce
carried over infection.

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