Beech Blight Aphids (Grylloprociphilus imbricator, family Aphididae) have been with us since the beginning of the growing season, gradually increasing their numbers and spewing out the processed sap of American beech (Fagus grandifolia), their primary host. However, they become most obvious in late summer to early fall when their colonies reach their maximum size.
The aphids are burdened with a misleading common name that doesn’t reflect their actual impact. They cause little to no damage to the overall health of infested American beech trees; however, “beech blight aphid” is the official common name the Entomological Society of America assigned to the species, so we’re stuck with it.
On the other hand, thanks to an imaginative interpretation by Erik Draper (OSU Extension, Geauga County), we’ve been calling this aphid the “boogie-woogie aphid” since a 2006 BYGL report (BYGL 2006-23, 9/7/06). This unofficial common name is more appropriate and descriptive since it describes the aphid's odd behavior in response to a perceived threat.
Large numbers of these native aphids gather in prominent groups that are commonly called "colonies." The colonies may include thousands of aphid nymphs that exude tufts of white, wool-like filaments from their posterior ends. They look like they’re sprouting cotton balls from their rumps. Collectively, the cottony material makes the colonies look like a jumble of white, fluffy material lining the twigs and branches of American beech. Large colonies commonly spill over from the stems onto leaves.
When disturbed, the entire colony will shake their woolly rear ends like they’re doing the boogie-woogie. I believe no other insect upstages beech blight aphids in entertainment value. Four years ago, I uploaded a YouTube video featuring the dance routine of the boogie-woogie aphids.
Dancers with Stilettos
Beech blight aphids have three lines of defense against predators and parasitoids. Their woolly coats serve as the first line of defense by hiding their soft bodies beneath a dense mass of waxy filaments.
It’s speculated that the mass-wiggling of beech blight aphids serves as the second line of defense by distracting or dissuading predators and parasitoids from focusing on single individuals. Defense strategies against predators that involve the collective movements of potential prey are well documented in other animals, although I could find no published research where this defense theory was tested with this aphid.
A paper published in 2001 described a more ominous third line of defense applied by beech blight aphid nymphs. The nymphs are highly aggressive against predators and will mass attack using their stiletto-like mouthparts to inflict serious damage to their assailants.
I’ve experienced their piercing defense firsthand while taking pictures. While their stabs produced more of a burning sensation rather than a sharp pain, it was certainly noticeable.
Aggressively attacking predators is uncommon behavior for most aphids. In response to a threat, aphids may emit a chemical message called an “alarm pheromone,” causing recipients to execute the Monty Python survival strategy: “Run Away!, Run Away!”
Most aphids are on the receiving end of animal aggression, serving as food for a wide range of predators, just like wildebeests are a food item for lions, cheetahs, leopards, etc. However, imagine an upside-down Syfy world with large numbers of wildebeests swarming to attack lions and leopards on the Serengeti.
The beech blight aphid isn’t the only woolly aphid that swarms threats. The sugarcane woolly aphid (Ceratovacuna lanigera), found in Southeast Asia, also attacks predators and parasitoids. A paper published in 1989 showed that the aphids emit an alarm pheromone, causing early and middle-instar nymphs to behave as soldiers by assaulting threats. However, the same pheromone causes late-instar nymphs and adults to flee. In other words, they send the children to fight while the adults and teenagers run away.
A Wolf in Sheep’s Clothing
While taking shots of beech blight aphids recently, I spotted a wolf in sheep’s clothing. I mean that literally. The “wolf” was the larva of a green lacewing (family Chrysopidae). It was one of the “debris-carrying” lacewings that camouflage themselves from other predators by carrying around bits of detritus that commonly includes the bodies of past victims. It’s an interesting take on “you are what you eat.”
Lacewing larvae have large, hollow, sickle-shaped mandibles that extend forward from their heads. They seize their prey with their mandibles and inject saliva that includes strong digestive enzymes. The enzymes liquify the innards of their prey, which is commonly aphids, so the lacewing can enjoy an insect Slurpee.
I have no idea how the lacewing larva was escaping detection and attack from the beech blight aphids. However, I assume it has to do with the lacewing’s stealthy hunting behavior, perhaps coupled with its disguise and the aphids not being terribly bright. I would think a pile of dead bodies trundling around would be an odd sight.
On a side note, Lacewings (order Neuroptera) are delicate insects named for their elaborate lace-like wing venation. Ohio is home to members of two families: green lacewings (family Chrysopidae) and brown lacewings (family Hemerobiidae). The larvae of all species are voracious predators.
A common error is to inadvertently call lacewings “lace bugs,” and vice versa. I’ve done it myself. It’s an easy mistake given that both names reference lacy wings. However, lace bugs are plant pests, while lacewings are predators; they are good. I keep it straight by remembering, “Wings are good, bugs are bad.” Maybe that just works for me.
Mounds of Moldy Poo
Another common feature of beech blight aphids is the appearance of weird-looking mounds of fungal growth beneath the aphid colonies. The accretions are linked to the copious quantities of honeydew excreted by the aphids.
Like many other sap-sucking insects, such as soft scales, aphids insert their piercing-sucking mouthparts into phloem vessels. They tap plant sap to acquire both carbohydrates, which provide energy, and amino acids, which are the building blocks for proteins and enzymes.
However, the phloem sap holds only trace amounts of amino acids compared to vast amounts of dissolved carbohydrates. This means the aphids must process a large quantity of sap to extract the necessary amino acids. They discharge the excess sugar-rich liquid from their anuses in the form of “honeydew," which is just a nice name for aphid diarrhea.
Beech blight aphids are prolific producers of honeydew. Even though the aphids are usually confined to just a few branches, it is common for sidewalks, parked cars, outdoor furniture, slow-moving gardeners, etc., beneath their gatherings to become covered in sticky goo.
The sooty mold fungus, Scorias spongiosa (Ascomycete), has an obligate relationship with honeydew exuded out of the rear end of beech blight aphids. It’s why the fungus is sometimes called the “beech blight aphid-poo fungus.” However, the sooty mold may also colonize honeydew produced by a few other woolly aphids, such as the woolly alder aphid (Prociphilus tessellatus), which is also known as the maple blight aphid owing to its alternate host.
The fungal growth of this unusual sooty mold begins like most sooty mold fungi; it grows as a dense, black, "fuzzy" mat on top of the honeydew. However, over time, the mat thickens into a brownish, furry mass.
The sooty mold is commonly found blackening the leaves of understory plants as well as the lower trunks of infested trees, where it appears bluish-black. Spotting patches of sooty mold beneath American beech trees is a good way to detect beech blight aphid colonies.
The fungus eventually progresses into a growth phase that is unlike most sooty molds. It produces spongy (= spongiosa), golden-yellow heaps that rise above the leaf or twig surface. The odd-looking fungal growths look like nothing else that would commonly be associated with aphids or honeydew, although it does attract wasps and flies in search of a sugary meal.
The fungal accretions may rise to impressive heights by the end of the season, as shown in the images below, taken on October 1. Some appear simply as mounds beneath the colonies, while others can acquire bizarre, almost creature-like forms.
During the winter, the accretions turn coal-black and may remain evident through much of the following spring and early summer. The black masses are sometimes mistaken for more serious plant problems, such as Black Knot fungal galls that occur on members of the Prunus genus. However, unlike the stem-cankering black knot fungus, the sooty mold fungus does not cause damage by invading the stem, as illustrated in the image below.
Digging Deeper
I have no idea why these aphids have “blight” in their common name other than their penchant for appearing as multitudinous white masses on American beech, or for the odd-looking fungal accretions on branches and leaves. Trees seldom have more than a few colonies that are confined to individual branches. Although I’ve observed dieback of the affected branches, the few branches lost are unlikely to harm overall tree health.
However, the aphids may have an indirect impact on forest regeneration. A study published in 2014 revealed a link between these aphids and decreased growth and survival of tree seedlings beneath heavily infested trees. The study described it as a “cascading effect” associated with the triumvirate of American beech, beech blight aphids, and the unique S. spongiosa fungus.
The beech blight aphid fungus will grow where woolly aphid honeydew is deposited on the leaves of understory tree seedlings. The authors of the 2014 study observed the recurrence of the aphids on the same trees year after year. They documented small but significant differences in seedling survival and growth between seedlings that experienced heavy black sooty mold colonization and seedlings free of the sooty mold growth. The seedlings tested included American beech as well as red maple (Acer rubrum), tuliptree (Liriodendron tulipifera), sycamore (Platanus occidentalis), mockernut hickory (Carya alba), and white oak (Quercus alba).
According to a study published in 1984 on the life history of beech blight aphids, the aphids will colonize the roots of baldcypress (Taxodium distichum). The study noted that the aphids can remain on baldcypress and are not required to spend part of their life cycle on American beech, or vice versa. Regardless, American beech is still considered the primary host, and baldcypress is the secondary host for this native aphid. The authors of the study did not document any negative impacts on the overall health of baldcypress. Also, the study focused on baldcypress in the southern U.S. with no mention of whether or not the aphids commonly colonize baldcypress in northern forests where American beech is more prevalent.
Finally, don’t confuse the beech blight aphids with the Woolly Beech Aphid (Phyllaphis fagi), which only occurs on European beech (F. sylvatica) and its cultivars. Another important difference is that while beech blight aphids will occasionally overrun leaves adjacent to the stem colonies, they do not occur as colonies confined to leaves. Woolly beech aphids are confined to leaves but will occasionally creep onto the stems where the infested leaves are attached.
Selected References
Aoki, S., U. Kurosu, and C.D. von Dohlen. 2001. Colony defense by wingpadded nymphs in Grylloprociphilus imbricator (Hemiptera: Aphididae) The Florida Entomologist. 84:431–434. doi: 10.2307/3496504.
https://journals.flvc.org/flaent/article/view/59670
Arakaki, N. (1989). Alarm pheromone eliciting attack and escape responses in the sugar cane woolly aphid, Ceratovacuna lanigera (Homoptera, Pemphigidae). Journal of Ethology, 7(2), 83-90.
https://doi.org/10.1007/BF02350028
Cook-Patton, S.C., L. Maynard, N.P. Lemoine, J. Shue, and J.D. Parker. 2014. Cascading effects of a highly specialized beech-aphid-fungus interaction on forest regeneration. PeerJ, 2, e442.
https://doi.org/10.7717/peerj.442
Crew, B. 2012. Dancing woolly aphids will probably stab you. Scientific American Blog Network. Posted September 12.
https://blogs.scientificamerican.com/running-ponies/dancing-woolly-aphids-will-probably-stab-you/
Michaud, J. P. (2022). The ecological significance of aphid cornicles and their secretions. Annual Review of Entomology, 67(1), 65-81.
https://doi.org/10.1146/annurev-ento-033021-094437
Reynolds, H. T., & Volk, T. (2007). Scorias spongiosa, the beech aphid poop-eater. Tom Volk’s Fungus of the Month, Sept. 7.
https://botit.botany.wisc.edu/toms_fungi/sep2007.html
Smith, C.F., and H.A. Denmark. 1984. Life history and synonymy of Grylloprociphilus imbricator (Fitch) (Homoptera: Aphididae) The Florida Entomologist. 67:430–434. https://www.jstor.org/stable/3494723
