> > I know Randy (and doubtless others) advocate caution in interpreting a
> number of studies that used high
> doses.
>

The authors used two different methods of dosing the bees--acute or
chronic.

Their testing involved feeding caged captured foragers treated syrup, and
then gluing them to a clever flight mill, and measuring how long it took
them to fly to exhaustion, and how fast they flew.  The bees were fed no
additional syrup during the flights.

*Acute exposure experiment*

OK, for this "acute" exposure, the bees were individually fed the amount of
118 ppb TMX in syrup that the authors calculated that they'd use for their
energy requirements in an hour of foraging; this worked out to be about a
third of a lethal dose.  Yet those bees kicked butt at foraging (not
unexpected after having been given a strong stimulant):

 "In the acute experiment, foragers consumed a single sublethal dose of
1.34 ng and subsequently increased their mean flight duration and flight
distance by 78% and 72% in comparison with control bees, respectively."

 The authors explained, however,  that we should discount this observation,
since:

"However, this increase in flight duration and distance is likely not
beneficial because, at similar doses, TMX and other neonicotinoids cause
flight disorientation."  But the authors did not test to determine whether
that actually occurred with bees so dosed in their experiment.

*Chronic exposure experiment*

Field-collected foragers were placed in groups in cages (number of bees per
cage not specified), and then fed TMX in sugar syrup at 0, 32.5 or 45.0 ppb
concentration.

The bees were not given any free choice as to syrup.  The mean dose per bee
was then calculated by dividing the amount of syrup consumed by the entire
group of bees in the cage over time (making the assumption that all bees in
the group consumed roughly equal amounts of the syrup).

The 32.5 and 45 ppb concentrations used are far higher than "normal"
field-realistic concentrations in the nectar of seed-treated plants, or of
plants foliar-treated by label directions.  I'd thus hesitate to make the
claim that the doses tested were "field realistic."

In this chronic feeding experiment, exposure to TMX at 1.96–2.90 ng/bee per
day appeared to reduce tethered bee flight distance by 56%--meaning that
the bees for whatever reason stopped flying earlier than did bees fed pure
sugar syrup.  The authors then extrapolated that:

"Based upon our results, we likewise predict that bees foraging on
neonicotinoid-treated fields for just one or two days will then fly more
slowly and in a reduced area. This behavioural alteration should reduce the
pollination service provided to plants, nectar and pollen collection for
the colony, and the nutritional biodiversity of collected pollen for the
colony.

In real life, however, it's been shown that foragers generally avoid
flowers with high concentrations of neonics, and forage elsewhere.

Oddly, the authors cite, and then dismiss a study that found conflicting
results when another neonic was tested:

"However, there was no significant effect of imidacloprid alone on honey
bee flight ability, and flight velocity was not affected even when bees
were exposed to both Varroa and imidacloprid."

What scientists look for is consistency and replication of results.  The
above is a red flag.

The authors, in an attempt to interpret their own results, go into
speculation:

"Why did acute vs. chronic exposures lead to opposite effects? Short-term
hyperactivity may lead to longer-term muscular exhaustion or energetic
depletion."

I don't understand why they'd mention "energetic depletion," since energy
comes from the sugar in the nectar.  In real life, the foragers wouldn't be
tethered to a flight mill, and would likely seek additional nectar should
they begin to run short on energy.

All in all, this is an interesting study, and good information on a flight
measurement device.  But I'd hesitate to draw firm conclusions from it
regarding what actually occurs in the field.  I'm not about to defend any
insecticide, but I'd be cautious about drawing conclusions based upon this
experiment.  One reason is that if the flight ability of bees were in "real
life" that strongly affected by field-realistic doses, one could easily
measure that effect by weighing free-flying hives to determine overall
foraging success.  To the best of my knowledge, no one has observed an
adverse effect on colony weight gain at field-realistic doses.

-- 
Randy Oliver
Grass Valley, CA
www.ScientificBeekeeping.com

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