The clay acts a a barrier, so
is basically inert as far as the bee is concerned. Only issue I would have
is if it enters the hive as a pollen substitute, but that would be no
different than a lot of stuff bees bring in as "pollen".

 
 
Clays and Dusts have long been used a insecticides, and as barriers.  With bees and dusts, particle size, electrostatic charge, dessicant properties, and abrasiveness all affect whether the substance is likely to adversely impact bees.  Fine particles can get into the trachea.  Charge alters adhesion.  Dessicants are targeted at the gut and at the soft tissues or larvae and pupae.  Abrasiveness also targets gut and soft tissue.

When MT St Helen's erupted, ash drifting into old, warped, poorly fitting hive parts adversely affected bee brood.  Newer, tighter equipment offered more protection - less places for dust to get in.  

We did a lot of testing.  Fine powders get into the trachea and smoother.  A variety of properties of the ash affected absorption, adsorption, and stickiness - not only for insects, but even on surfaces like pine needles.

In spruce budworm, dust in diet affected nutritional value, but had a positive effects in the control of Nosema in budworm.  In bees, ingested ash had a detrimental effect to bees - the gut of a budworm is obviously less affected by dessicant/abrasive properties than those of bees.   In both budworm and bees, larvae are the most vulnerable to the dessicant/abrasive properties.

Biggest issue in the question of clay - how the bees might be exposed.  As a dry dust?  As a wet slurry?  Or is it simply laying on a surface as a barrier?



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