Over the years, the late-season Beech Blight Aphid (Grylloprociphilus imbricator) has waltzed through the pages of the BYGL on an annual basis. The aphids have a single venue; they are only found on the twigs and branches of American beech (Fagus grandifolia).
Past BYGL-reviews of their yearly return engagements have had nothing to do with harm to their namesake host since they appear to cause little damage. The aphids usually re-take the BYGL-stage because of their obvious, snow-white appearance, their heavy production of honeydew ... and their entertainment value.
Beech blight aphid nymphs enshroud themselves in a profuse mass of white, wool-like filaments. Large numbers these "woolly aphids" will gather together in prominent colonies on twigs and branches of American beech trees. When a colony is disturbed, the aphids pulse their posterior ends in unison. This peculiar behavior has been accurately described in past BYGLs as making the aphids look like "dancing dust balls doing the boogie-woogie." This behavior has earned the aphid the alternate common name of the "boogie-woogie aphid."
It is speculated that this mass-wiggling is designed to distract and dissuade predators and parasitoids from focusing on single individuals. However, research has shown that the nymphs are highly aggressive against predators. If doing the boogie-woogie doesn't work, the nymphs will mass-attack predators causing serious damage with their piercing-sucking mouthparts that are normally used to extract sugary juices from the tree's phloem vessels. So, their group wiggling could be viewed as a war dance.
Aphid colonies are usually relegated to a few branches. However, they are prolific producers of honeydew causing branches, sidewalks, parked cars, slow-moving gardeners, etc., beneath the colonies to become covered in sticky goo. Indeed, aphid colonies are often found by observing circular or semi-circular spots of sticky honeydew on hard surfaces beneath infested trees. The honeydew on leaves and branches may become heavily colonized by black sooty molds.
Indeed, the fungus (Scolias spongiosa (Ascomycete)) is exclusively associated with the aphid and is commonly called "Beech Blight Sooty Mold." It is also sometimes called the "beech blight aphid poop eater" because of its food supply and obligate relationship to the aphid; the fungus only grows on honeydew produced by the beech blight aphid. The fungus starts out behaving like most sooty mold fungi; it grows as a dense, black, "fuzzy" mat on top of the honeydew. Over time, the mat thickens into a brownish, furry mass. Then the fungus progresses into a growth phase that is unlike most sooty molds; it produces a spongy, golden-yellow heap that may rise 1 - 2" or more above the leaf or twig surface. The odd looking fungal growths look like nothing else that would commonly be associated with aphids or honeydew. It may also attract yellowjackets and baldfaced hornets in search of a sugary meal.
Adding to the diagnostic challenge, the fungus will grow anywhere that beech blight aphid honeydew is deposited. So, thick fungal accretions may appear on the leaves and stems of understory plants that are not hosts to the aphids. During the winter, the fungal accretions turn coal black and may remain evident through much of next season. They are sometimes mistaken for more serious plant problems such as black knot on prunus.