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From:
Jerry Bromenshenk <[log in to unmask]>
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Informed Discussion of Beekeeping Issues and Bee Biology <[log in to unmask]>
Date:
Thu, 3 Aug 2017 00:48:49 -0400
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>Karl von Frisch was always very critical of his own experimentation>  
There's no doubt that he was a brilliant man, but he wasn't always careful.  
An often quoted example is that he pronounced that scent detection by bees was not much better than a human's nose.  That 1919 paper was based on a flawed manner of presenting the odors to the bees and a surprisingly small sample size for the human nose comparison.  
V. Frisch  concluded that bees conditioned to bromstyrol and to methyl heptenone readily recognized these chemicals in 1:2,000 dilution in liquid paraffin, but not at 1:20,000.  Ribbands 1953 repeated this work using a better method of scent presentation.  He found that bees perceived methyl heptenone in 1:40,000,000 dilution.  Honey bee perception of various other organic chemicals tested by Ribbands ranged from 1:100,000,000 (phenyl ethyl alcohol, benzyl acetate, methyl benzoate) to 1: 5,000,000,000 (linalol). 
Honey bee thresholds of detection were 1 to 10 orders of magnitude below those of humans; bees reliably detecting scents at concentrations imperceptible to humans.    When Ribbands looked at floral scents, the bees often did even better.  It appears that von Frisch's odor presentation method produced an overly conservative estimate of the Limit of Detection for honey bees.  Using a better method, Ribbands clearly showed that bees were better at scent detection than von Frisch's study indicated.   Although Ribbands questioned the value of comparing bees to humans, he at least used test data for humans based on large numbers of individuals, who not unexpectedly displayed individual variation in odor perception.  For a chemical such as methyl heptanone, Ribbands reported that the most sensitive 25% of humans tested was 1:1,000,000. 
von Frisch concluded that the thresholds of perception for bees and humans were similar based on his wife's and his own perception thresholds.   In essence, von Frisch and his wife stood in for all of the rest of the humans in the world - rather a small sample size.

When we set out for DARPA to see if bees could detect vapors of explosives leaking from buried landmines - we weren't the first scientists who had been approached by DARPA.  Every other bee scientist told DARPA that bees didn't have a very good sense of smell, not much better than humans, except possibly with the exception of some floral scents and pheromones.  That myth is promulgated in numerous publications, even by well recognized experts in the field - I suspect many of you have seen this myth - just shows that one should always go back to the original research.  Ribbands disproved both conclusions of the von Frisch's and his 'reward' was that his own work was misquoted to add the caveat - except for a few floral scents.

Our own research, verified by a full year of double-blind testing with videos of all trials showed that bees could reliably detect chemicals like 2-4DNT at vapor concentrations down to a few (less than 10 parts per trillion), and we have video of bees searching for vapor plumes of 2-4DNT, locking onto the plume path 10 yards (meters) or more away from the buried land mines.  At 12" above the surface of the ground the vapor concentrations of this chemical were in the 5-15 pptr range, mostly 5-10.   Given that wind, vegetation, etc. have a pronounced effect on vapor plume dispersion, at ten or more yards away, even the most conservative model showed that the detection limit for this explosive break-down product was somewhere in the parts per quadrillion.   We don't know how low the actual detection threshold is for 2-4 DNT, the analysts had to draw 30 minute samples using sample tubes and pumps located 12' above the buried land-mines, just to be able to detect this chemical at PPTr levels.  The bees did the same easily with instantaneous recognition!   We've even done some comparisons with dogs - which is better - almost impossible to tell since no one has field instrumentation equal to the LODs of either animal.
 
In other words, bees are way better than even Ribbands thought.  It's really hard to visualize LODs at these levels.

The best way that's I've found to comprehend enormous numbers is the MegaPenny Project.  How big is a pile of 1 million, 1 trillion, 1 quadrillion pennies- see them here http://nanospace.molecularium.com/attractions/mega_penny/  I suggest that you click the button to turn-off the music.  The original web site seems to have disappeared, but the images have been retained in this slide show.  It's well worth a look.   For example, 1 trillion pennies is a 273 ft cube, weighing 3, 125,000 tons.  Stacked in a one penny wide column, the trillion pennies would rise 986,426 miles. Our bees easily finding the equivalent of 1 - 10 pennies in the pile is impressive.  1 quadrillion is a staggering 2,703 ft cube, stacked vertically, the pennies would tower 986,426,768 miles!  1 quadrillion pennies would cover the earth's surface twice.  Imagine, the Sears Tower occupies a space of 2.6 trillion pennies.  

 

 

 
 





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