Randy   Did the researchers have equal numbers of control colonies with the same feeding and handling, minus the pesticide?
I'd expect the handling alone to be a significant stress/mortality factory.   Years ago, with my observation hive, I tried duplicating studies of dosing marked bees and returning them to hive.  The idea was to track forager longevity.   I noticed highly variable losses of marked bees, depending on nectar flow, size of colony population, time of year.   Variability was so high as to make the procedure unusable. 

Many years later, we showed the bees can detect the odors of some chemicals at vapor levels as low as Parts per Quadrillion.  

When we were working on our acoustic app, we dosed individual forager bees with incredibly low levels of toxic chemicals -   the guard bees routinely attacked a large percentage of the dosed bees returning to their original hives. 

Finally, Michelle Taylor in her thesis work made up tea bags containing a malathion treated, inert substrate.  The bees stung the bags hanging inside the hive btw frames.
Handling stress and handling/dosing odors are a factor of any dose and return trial. 




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