Answer: I would bet money that your magnolia is covered with aphids or scale insects. Those insects secrete huge amounts of a sweet waste product called "honeydew." This substance is extremely attractive to all manner of other insects. Ants, in fact, will defend aphid and scale insect colonies in exchange for a monopoly on the honeydew. The honeydew also drips onto the foliage, so the wasps and flies are eagerly lapping it up off the surface. So, if you control the aphids (with insecticidal soap sprays) or the scales (with a winter spray of horticultural oil) you should eliminate the honeydew and the bees, hornets and flies will no longer be interested in your magnolia bush.
Best wishes with your landscape!
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