Asian Woolly Hackberry Aphid
You need a magnifying glass to see the insect under all that "snow."
Chances are you may not recognize this critter up close. Where the Asian woolly hackberry aphid is most prevalent in early fall — the Southeast and parts of the southern Midwest, Texas and California — residents have called in with reports of "flying snow" or "flying cotton." These tiny (2 mm. long) insects are covered with a thick layer of bluish-white waxy wool. If it weren't for the insect's antennae, you'd need a magnifying glass to see that there's a bug under all that "snow."
In the spring and summer, the females are parthenocarpic — that is, they reproduce without males; they give live birth to their young, and there can be multiple generations. The females can be either winged or wingless. In the fall, the winged males are produced, mating with the females to create eggs that will overwinter.
A native of China, this woolly aphid was accidentally brought into the U.S. in the late 1990s and can be found on sugarberry and hackberry trees. It's not usually considered a serious pest of the trees (its host plants have survived repeated infestations), but it produces large quantities of sticky honeydew, which can in turn promote the growth of sooty mold. So the aphid isn't an agricultural or a garden pest, but it can be an inconvenient nuisance if you happen to have hackberries that shade a walkway, driveway or city street.
In cities where the Asian woolly hackberry aphid has been problematic, an application of imidacloprid has been found to be effective.