Glen has raised an interesting question. Although I have nothing other than my own experience and anecdotal data to support what follows, I believe the proximate composition of the yeast may well be responsible for the development of the "dysentery" symptom. More so than any possible contamination by bacterial organisms associated with intestinal disorders generally, since as you have noted,the yeast manufacturers are obviously well aware of this possibility and have quality control in place to prevent it.

     Bees that are "under-nourished" to the point that a beekeeper will resort to the expense of feeding them with protein supplements, (I am loathe to use the phrase "starving", although I fear this may often be the case), are already under severe stress. Under these conditions, they are very susceptible to express the symptoms of many diseases or sicknesses, which under good nutritional conditions they are able to fend off. Bees of course are not unique in this behaviour, as managers of flocks of sheep, herds of cattle, and even medical practitioners will attest.
   
 Consequently when reintroducing the bees to nutritious (we hope) diets, it is necessary to be very careful, particularly in regard to protein and fat levels. It is not uncommon with bees, as with most other creatures, to induce severe intestinal disturbances when the diet is suddenly changed from a dearth to a rich food intake. Recommended practice here in Australia, is to feed the bees dilute sugar syrup for 5 to 7 days, prior to introducing protein supplements, and most importantly, IRRESPECTIVE of whether or not they have ripened honey stores in the hive.

    There are many possible causes for the dysentery symptoms. A very common and significant cause can be Nosema disease. Unfortunately, the intestinal parasite which causes this disease may well benefit significantly from the feeding program too. Feed the bees and you feed the nosema, so this condition may worsen before it gets better.

    Nutritional imbalance can also cause problems. High protein (40% or more) and low fat levels ( 1.5% or less), as can often be found in dried yeasts available commercially, are substantially different to the levels in the pollens of European plant species that European bees evolved with ( which are more in the region of 25-28% protein and 5-8% fat). And this is without taking into consideration the variations in the amounts of individual amino acids and fatty acids which make up those proteins and fats! Then we also have to consider vitamins and minerals (and there are lots of those). As you can see feeding bees is not a simple matter.

     Carbohydrate feed supplementation is fairly well understood now, and most of the practical problems have been resolved and  widely communicated. However the situation with proteins and fats is still far from resolved. Whilst there are a number of proprietary feeds on the market, each with their devout advocates, in truth the "jury is still out" on them.

    So Glen, feeding your bees dried yeast may help them one way and hurt them in another. There is much research needed here. Beekeepers globally need to devise and support methods to raise funds to promote this research. (Any brilliant ideas out there?). I would love to be able to point you in a more immediately helpful direction, as I too am faced with the same problem. In the past I have inadvertently done my bees more harm than good on a number of occasions when I have tried to assist them in times of dearth. But I have learnt a lot in the process, and these days my girls all stand around expectantly in a big circle when I lift the lid, so they haven't given up on me yet!

Peter Detchon
Western Australia
(Still feeding and wondering when the pollen flow will start)

   

    

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