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Oxalic crystals on bees after vaporization

Crystals from oxalic acid vaporization on bees’ bodies

Randy Oliver

February 2020

In order to determine how OA crystals settled on bees’ bodies after an OA vaporization, I set a graduated microscope slide and a number of dead bees under a 16-oz inverted plastic cup.  I injected OA vapor briefly into a hole at the top of the cup, and then allowed the fog to cool and settle for a few minutes before removing the bees.

Too much vapor resulted in snow-white bees and a white slide covered by a layer of OA crystals.  By trial and error, I found how much vapor to inject to reach what appeared to be a field-realistic “dose” of OA on the bees:

The bees and slide looked like this after allowing a light OA fog to settle on them.  The bees were not noticeably “whitened.”

Close up of a bee.  You can see the white crystals on its wings and “hairs.”


A closer view of the same bee, OA crystals mainly on the tips of these thoracic setae.

I titrated the amount of OA on the bee’s bodies.  It was roughly equivalent to 0.0001 g/bee (equivalent to 5 ml of medium-strength OA applied to a frame interspace containing 2000 bees, or 2 g OA vaporized onto 20,000 bees).  So it appears that this amount of OA crystals is field realistic.  I’ll confirm with full-hive vaporizations.

A view of the slide at 400x.  OA crystals, dark field.

OA crystals on the same slide, light field (crystals look black); scale is 0.01 mm gradations.

Crystals on the abdominal setae.

Close up of OA crystals.

The bee’s wing at 100x.

The bee’s antennae.

Setae at 400x.

The above photos were of dead bees vaporized in the cup, as shown.

Photos after in-hive vaporization

The photos below are from the few dead and dying bees at the entrance of a hive an hour after vaporization with ProVap 110.  Note that there are far fewer OA crystals.


A lighter coating of OA crystals.

When I viewed bees from the inside of the cluster 10 minutes after vaporization (to allow the crystals to attach to the bees), I surprisingly couldn’t see any crystals on the bees, and the bees surprisingly tested negative for OA residues – I am following up on this observation!

All above photos reduced in size.  Contact me for full-resolution.