Hi:  We make the pollen grids - too costly for general use.  Years ago, I
found some beekeepers using a European plastic grid with star-shaped
holes.
 
If anyone knows where I could get some of these, I would be thrilled.
 
We use plastic for our experiments because the metal grids add zinc and
other contaminants to the samples that we analyze for environmental
pollutants.
 
 
As to why the bees varied in size in our Seattle studies - I am sure
foundation supplier variability, old versus new comb, and maybe even
races of bees entered into the equation.  We didn't address the why, only
which trap worked.
 
The "fat" bees after dropping 3,000 feet in elevation is a mystery.
 
Thanks
 
Jerry