"I can see another research project on the horizon"

Hello Peter,
The subject is vast as not only the aphids are to be considered but also the plants or the trees.

This is difficult to identify the exact root cause without knowing the foraging tree, but it is well known in France, that honeydew coming from pines forest needs to be removed from our hives before winter. Dysentery and high mortality will occur if this honey is not replaced by syrup.
One of the cause is linked to high content of polyosides (coming from the elaborated sap circulating in the phloem of the tree and colected by aphids). The honeydew is produced by all kind of insects sucking the sap and the sugar contain is different compare to floral honey with presence of trehalose and melezitose. In the black forest (Germany) and in Vosges (France), it is sometimes impossible to extract honeydew because of the high contain of melezitose (8%) from Larix, they call it concrete honey. If this honey stays in the hive the colony will starve on it, enable to dissolve this sugar. Usually the moisture of honeydew is never high (below 17%) this is because warm weather is needed for the bugs to proliferate, also if it rains the honeydew will be washed away.
The second cause is linked to the impurities inside honeydew such as spores, fusarium microconidia, and other pollution present in the air. The sticky sugars will trap anything. All of these impurities are easily detectable under the scope. See this publication to understand spores association : https://core.ac.uk/download/pdf/42945238.pdf
Again the honeybees need to eliminate these wastes outside the hive and there is no problem in summer but, during winter it causes dysentery. Honeydew is not linked to nosema, but it can spread the desease of a few sick bees, when they are cleaning the feces on the frames.
Georges, France

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