Re the discussion on what temperatures are needed to kill AFB spores, I will detail results from two trials that I was project leader for.  There were two parts to the trials.  Firstly lab work and then field work. The work was funded by our Honey Bee Research and Development Committee.

There is an important point to take into account when looking at what temperatures are needed.  If the conditions are wet e.g. in honey, or water then the time needed is much lower than if it is dry e.g. dry boxes in an oven.

At 100 degrees centigrade in the wet condition in ther lab, two experiments showed times of 30 and 35 minutes to kill the spores.  Death was determined by having no vegetative growth on J agar plates after 4 days incubation.  At 110 degrees, one experiment showed 30 minutes and at 120 degrees, one experiment showed 15 minutes.

In the dry condition in the lab, two trials at 110 degrees gave a time of 5 hours to kill the AFB and at 120 degrees it was 3 hours.  In a second trial, at 110 degrees it was again 5 hours and at 130 degrees, it was 3 hours to kill the spores.  So you can see there was a great varaiation between wet and dry.

Also the concentration of the spores affected the time needed.

If you look at the literature, you will find trials on the longevity of AFB in honey to range from 15 minutes to 5 hours and most of these were around 100 degrees.  In relation to beeswax, at 100 degrees one report is 19 hours, 88-118 degress is 4 hours and at 150 degrees, it was 20 to 60 minutes depending on spore concentration.

If you are boiling wax in water to melt it then, from our work I would think that there is not much chance of AFB being alive.  Another thought is that the spores are entombed in the wax and are not available to the bees.  In Australia, there has never been a reported case of AFB that has been attributed to beeswax as the primary infection source.

When we went to a timber drying kiln, we seeded 80 boxes with AFB spores and at the end of the run, which was exposure for 5.5 hours at 110 degrees, we had a 90% kill.  10% still cultured positive.  This was a dry heat condition.

In the second trial we exposed 104 seeded sites to 130 degrees for 4 hours in a commercial powder coating kiln.  This was dry heat.  We had a 70% kill with 30% being still cultured positive.

So you can see that we did not have success in the commercial or field situation with a 100% kill.  The question was raised as to whether the cultured spores were actually viable or whether they had been altered in some way by the heat.  We never progressed this aspect.

So I would put it to the list that it is possible to kill AFB spores in beeswax with normal refining processes provided the temperatures are held for the correct period.

Trevor Weatherhead
AUSTRALIA