Glyphosate in the News, or Turtles All The Way Down

NEWS FLASH 
Common weed killer—believed harmless to animals—may be harming bees worldwide
Sep. 24, 2018 , 3:00 PM https://www.sciencemag.org

¶

Glyphosate perturbs the gut microbiota of honey bees
Erick V. S. Motta, Kasie Raymann, and Nancy A. Moran

Glyphosate, the primary herbicide used globally for weed control,
targets the 5-enolpyruvylshikimate-3-phosphate synthase (EPSPS)
enzyme in the shikimate pathway found in plants and some
microorganisms. Thus, glyphosate may affect bacterial symbionts
of animals living near agricultural sites, including pollinators such as bees.

We demonstrated that the relative and absolute abundances of dominant gut microbiota species are decreased in bees exposed to glyphosate at concentrations documented in the environment. 

Glyphosate concentrations were chosen to mimic environmental levels, which typically range between 1.4 and 7.6 mg/L (Herbert, 2014), and may be encountered by bees foraging at flowering weeds. 

¶

Herbert LT, Vázquez DE, Arenas A, Farina WM (2014) Effects of field-realistic doses of glyphosate on honeybee appetitive behaviour. J Exp Biol 217:3457–3464. 

We studied the effects of field-realistic doses of GLY on honeybees exposed chronically or acutely to it.

Successful forager bees can become a source of inflow of nectar with GLY traces into the hive, which in turn could have long-term negative consequences on colony survival.  We speculate that successful forager bees could become a source of constant inflow of nectar with GLY traces that could then be distributed among nest mates, stored in the hive and have long- term negative consequences on colony performance. 

Due to the upscale in monocultures and genetically modified crops, aerial applications of GLY have become the most common application method and have widened its spread area (Giesy, 2000). 

¶

Giesy, J. P., Dobson, S. and Solomon, K. R. (2000). Ecotoxicological Risk Assessment for Roundup® Herbicide. In Reviews of Environmental Contamination and Toxicology, vol. 167, pp. 35-120: Springer, New York. 

The acute toxicity values observed for RU and glyphosate to honeybees (Apis
mellifera)  are given in Table 22. Tests using honeybees exposed to 100 µg/bee
of RU or glyphosate in the diet and applied topically were designed to mimic
secondary exposure of bees through the consumption of pollen or direct exposure
resulting from inadvertent overspray, respectively (HRC 1972). The dietary
and contact LD50s were >100 µg RU/bee. For glyphosate, the dietary and contact
LD50s were 100 and >100 µg a.e./bee, respectively. A general guideline has been
suggested for assessing toxicity of pesticides to honeybees (Felton et al. 1986).
A hazard ratio is derived from the formula (g active ingredient/ha)/(LD50 for
bees in µg/bee). Depending on the ratio, the risk to bees is as follows:

Hazard ratio <50 Low risk
Hazard ratio 50-2,500 Moderate risk (further assessment needed)
Hazard ratio >2,500 High risk (further assessment or mitigation needed)

Based on these data, the hazard ratio would be 4300/100  (for a 4.3-kg a.e./ha
application rate), or 43; this puts glyphosate in a low-risk category. No chronic
assessment was conducted for honeybees because of the large safety margin in
the acute assessment and the expected rapid decline in environmental exposure to this species.

¶

My comments:

> The metaphor of dwarfs standing on the shoulders of giants (Latin: nanos gigantum humeris insidentes) expresses the meaning of "discovering truth by building on previous discoveries".

In this case, I traced the logical chain from the most recent report implicating glyphosate and bee decline backwards via the references. As is often the case, the claims are based on references which do NOT support them. 

This phenomenon of supporting a hypothesis with prior hypotheses can be illustrated by this brief anecdote:

The lecturer had spoken about the nature of the Earth and the planets. Afterwards
a lady approached him, claiming she had a theory superior to the one he had
described. “We don’t live on a ball revolving around the Sun,” she said. “We live
on a crust of earth  on the back of a giant turtle.”

Wishing to be gentle towards the old lady, the lecturer asked: “And what does
this turtle stand on?” “You are a very clever man,” she replied, “to ask such a
searching question. But  I can answer it. The first turtle stands on the back  of a
second, far larger turtle.” “But what,” he went on politely, “does this second turtle
stand on?” “It’s no use, mister,” she replied, “It’s turtles all the way down.”

Gold, T.* (1975). After dinner talk: how not to do science. Annals of the New York Academy of Sciences, 262(1), 496-500. 

* Thomas Gold, Center for Radiophysics & Space Research. Cornell University Ithaca. New York 14850

¶

Which in turn is a corruption of an anecdote published some 140 years prior:


In my schoolboy days, when I loved better to rob bird's nests and plunder orchards than acquire knowledge, I have often deserted the school-room, and pursued the above mentioned vocations in the forest in my usual quiet manner. I recollect once, when having been lost in the intricacies of a wood, I stumbled upon a little hut. Being extremely thirsty, and rightly concluding that a spring would be found in its vicinity, I wended my way thither. I found it occupied by an old woman, of whom I requested a draught of water. It was soon furnished; and when I had dispatched it, was overwhelmed with questions. 
	“Arn’t you one of the 'Cademy boys?" enquired she.
	“Yes, marm,” was the reply. 
	“Well, I declare!” ejaculated the old woman. “They say you larn queer things down there—why, they say the world is round.”
	“The world, marm,” said I, anxious to display my acquired knowledge, “is not exactly round, but resembles, in shape, a flattened orange; and it turns on its axis once in twenty-four hours.”
	“I don't know any thing about its axes,” replied she, “but I know it don't turn round, for if it did, we'd all be tumbled off; and as to its being round, any one can see it's a square piece of ground standing on a rock.” 
	“Standing on a rock! but upon what does that stand?” 
	“Lauk, child! how stupid you are! there's rocks all the way down.”

Anonymous. (1838). The New-York Mirror, Volume 16.

¶

If you have read this far, you will note that the news report implicates Round-Up as harmful to bees based on "field realistic doses" -- always citing previous work. I haven't found where anyone has ever measured glyphosate levels in nectar or shown that it ever winds up in the honey bee food sources. In fact, it was declared to be a non-issue, because ingestion is so unlikely.

PLB





             ***********************************************
The BEE-L mailing list is powered by L-Soft's renowned
LISTSERV(R) list management software.  For more information, go to:
http://www.lsoft.com/LISTSERV-powered.html