>I wonder why collapse of colonies is what you consider to be the
significant neonic effect?

Good question, Christina.  I run a large number of controlled field trials,
for myself and for private parties with products (no, not pesticides) to
sell to beekeepers.  The question to me is of which metrics to take to
detect negative or positive effects of a product upon a colony.  IMHO, some
metrics (such as square inches of sealed brood) are a waste of time.  There
are only two metrics of interest to beekeepers--colony adult population and
colony weight gain (or loss).

The first is the result of the final calculus of all factors affecting
colony reproduction and average worker longevity (from egg to death at
whatever stage of development).

The second (weight gain) reflects the ability of the colony to muster up a
forager force and effectively and efficiently forage, as well as to
maintain a force of  mid age bees to build comb, process, and store honey.

Any factor that affects the colony reproductive rate, worker longevity, or
ability to effectively forage and convert nectar into honey will be
reflected in those two metrics.

The most severe effect will be colony dwindling or depopulation, the
inability to gain weight, or both.

Those of us who have played with modeling colony population dynamics
quickly learn that anything that reduces average larval survival or worker
longevity by even a little bit will have a huge effect upon overall colony
population (I'd be happy to show you graphs).  So in partial answer to your
question, if chronic exposure to a chemical has any negative effect upon
either larval survival, age of first foraging, or mean worker longevity,
the affected colony will quickly show that effect by either having its
growth slowed (or going negative) relative to a control colony.  This is
why I consider the comparison of the adult populations of the test and
control colonies to be so meaningful.  Collapse would be the most obvious
effect, but many researchers (Lu, Pettis, Krischek, among others) have
observed that colonies chronically treated with IMD during summer maintain
their populations relative to the control colonies.

But, you ask, how about sublethal effects that affect individual immune or
foraging performance?  Any negative effect upon individual immunocompetence
would quickly be exhibited in the "r" (intrinsic rate of increase) of the
colony (in the adult population) since pathogens are ubiquitous in all
hives, and would shorten the longevity of adult bees (quickly resulting in
a reduced colony growth rate).

Re the effects of neonics upon foraging performance, one need only speak
with Canadian beekeepers who make 300-lb crops of honey on seed-treated
canola--in which every drop of nectar and grain of pollen contain easily
measurable residues of clothianidin.  If those residues indeed had negative
effects upon individual forager longevity, navigation, or foraging ability,
there is absolutely no way that those colonies could make 300-lb honey
crops!

So in answer to your question, despite the clearly-documented negative
effects of high doses of IMD or clothianidin upon bees in the lab (and the
theoretical implications), controlled field trials and on-the-ground
truthing simply do not support the hypothesis that the concentrations of
neonics found in (at least) seed-treated canola exhibit any overall
negative effect upon colony performance (see the recent Cutler/Scott Dupree
study) or individual bee performance.

On the other hand, at concentrations in the nectar exceeding 50 ppb, there
are readily-observable negative effects.  But 50 ppb is better than 10
times the concentration that results in nectar from proper seed treatment.

>Also, what is the right way to look at "field dose" in your view?  If
foragers bring back amount X of some chem treatment, is that what you
consider to be the "field relevant" amount?

Yes.

Christina, I hope that I've answered your questions.  Please let me know if
you want more elaboration.

Your concerns about neurotoxicity and sublethal effects are well-founded,
especially for dust/foliar/landscape/ornamental uses of neonics.  But
ground truthing does not support the hypothesis that the residues in nectar
and pollen of seed-treated crops have substantial adverse effects upon the
colonial insect *Apis mellifera* (I am limiting this discussion to that
species alone).


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

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