On Sat, 9 Mar 2019 21:24:30 +0100, Predrag Cvetkovic <[log in to unmask]> wrote:


>honeydew, but it is the other type of honeydew. Oak honeydew is a product
>of the secretion of oak leaves, it is without the influence of insects.
>

We have honeydew on oaks here in NZ and some trees have far more honeydew and bees than others.  However here the source of the honeydew is a scale insect on the stems, but the leaves are covered with shiny nectar, the result of dripping from the scale insects.  Without close inspection, it just appears as though the honeydew nectar is forming on the leaves.

There's a couple of photos here showing a bee collecting honeydew on such a leaf and scale insects:
https://pbase.com/peterbray/image/106271602
https://pbase.com/peterbray/image/168914612

Incidentally, sap sucking insects (Hemiptera) are mining for protein to build their bodies.  Since sap has little protein, they have to process large quantities of it and thus exude the surplus (pass it out their anus).  Doing so presents a problem of the high osmolarity of the sap drying them out.  To solve this problem they use enzymes (probably in bacteria in their gut) to split the sugars in the sap and take out a water molecule and then tack this sugar onto the back of another, forming long chain sugars (oligosaccharides).  These are often indigestible in our upper intestinal tract and make their way to our lower intestines where probiotic bacteria digest them.

Regards,
Peter Bray

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