Thanks to listener Wayne Thomas, we have this good picture of bark aphids. Use it to confirm if you have an infestation.
These are not to be confused with bark lice, which are beneficial insects.
As most of the calls the radio program have confirmed, bark aphids are anything but beneficial ... they rain honeydew on everything below. Then, a black, sooty mold develops on the honeydew. Most calls seem to be from listeners either wondering why the tree seems to be dripping sap (actually the honeydew excrement from the aphid) or what's the unusual bug clustering on my tree limbs.
There are a couple ways to rid yourself of the problem.
First, blast them off with a water hose and treat the tree a day or two later with dormant oil spray.
If you want an immediate kill, go with malathion, isotox or orthene. I suggest a dormant oil spray a week later to insure you kill any eggs or nymphs that may have been protected during the insecticidal spray.
And here's something to consider: if the honeydew is dripping harmlessly on nothing below, entomologists say this are a short-lived insect that will go away on its own.