I was surprised over the weekend to come across a horde of Beech Bligh Aphid (Grylloprociphilus imbricator) nymphs on their namesake host in southwest Ohio. This aphid spends the winter in the egg stage and I had assumed they had completed their seasonal development.
Beech blight aphid nymphs exude tufts of white, wool-like filaments from their posterior ends. Large numbers of these native aphids gather together in prominent groups that are commonly called "colonies" on the twigs and branches of American beech. The colonies appear as masses of white, fluffy material adorning the twig and branches of their namesake host.
When disturbed, the entire colony will pulse their woolly derrieres in unison in what appears to be a synchronous samba. This peculiar behavior has earned the aphid the alternate common name of the "boogie-woogie aphid." I believe no other insect upstages beech blight aphids in entertainment value. To see what I mean, just Google "boogie-woogie aphid" to watch several YouTube videos.
An Aggressive Aphid
It is speculated that the mass-wiggling of beech blight aphids distracts or dissuade predators and parasitoids from focusing on single individuals. Although I could find no published research where this defense theory was tested with this aphid, the collective motion of prey to lower the targeting success of predators has been documented with other animals.
On the other hand, research has been published showing beech blight aphid nymphs practice another far more unusual type of defense strategy. The nymphs are highly aggressive against predators and will mass-attack using their piercing-sucking mouthparts to inflict serious damage to their assailants.
This is uncommon for aphids. In my teaching presentations, I sometimes compare aphids to other herbivores like wildebeests to drive home certain points regarding predator/prey relationships. However, imagine the upside-down Syfy world presented by wildebeests swarming over lions on the Serengeti.
Harvester Butterfly (Feniseca tarquinius, family Lycaenidae) caterpillars also invoke a similar inverted order to things. They are the only strictly meat-eating butterfly caterpillar found in the U.S. I posted an Alert about these predacious caterpillars a few weeks ago after observing them snarfing Woolly Alder Aphids (Prociphilus tessellatus) [see White-Haired Alders and Meat-Eating Caterpillars, October 14, 2019].
Harvester butterfly caterpillar may also be found creeping among colonies of other woolly aphids such as the Woolly Elm Aphids (Eriosoma americanum). However, the carnivorous caterpillars do not appear to hunt beech blight aphids. Perhaps the blight aphid's gyrations are a war dance!
You can read more about this fascinating stabbing behavior of beech blight aphids by clicking on the hotlinks beneath the publication titles below:
Dancing Woolly Aphids Will Probably Stab You
Colony Defense by Wingpadded Nymphs in Grylloprociphilus imbricator (Hemiptera: Aphididae)
Primary and Secondary Hosts
I've always written in past BYGL reports that this aphid is only found on the twigs and branches of American beech. While it's true that these aphids do not infest non-native beeches, this is only part of the host story.
According to the literature, beech blight aphids may also be found on Baldcypress (Taxodium distichum); however, they are not seen feeding in colonies on twigs and branches. A study on the life history of this aphid that was published in 1984 in Florida Entomologist reported that both wingless (apterous) and winged (alate) asexual (viviparae) beech blight aphids have been documented feeding on the roots of baldcypress.
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. However, American beech is still considered the primary host and baldcypress the secondary host for this native aphid.
Host Impacts and Moldy Matters
Despite their sinister-sounding name and penchant for appearing in large white masses, beech blight aphids cause little to no harm to the overall health of their beech host. I could find no studies investigating the impact of root-feeding on baldcypress.
Thus far, there also appears to be no link between this aphid and the enigmatic "beech leaf disease" (BLD). I've taken pictures of both together which could cause the casual observer to link the disease symptoms to the aphids. However, beech blight aphids are commonly found where BLD has never been reported.
The most obvious impact of the aphids is associated with their prolific production of honeydew. Even though the aphids are usually confined to just a few branches, it is common for sidewalks, parked cars, outdoor furniture, etc., beneath their gatherings to become covered in sticky goo. Indeed, aphid colonies are sometimes discovered by observing circular or semi-circular spots of sticky honeydew on hard surfaces beneath infested trees.
The sooty mold fungus, Scorias spongiosa (Ascomycete), has an obligate relationship with honeydew produced by beech bight aphids as well as a few other woolly aphids including the aforementioned woolly alder aphid which is also known as such as the maple blight aphid owing to its alternate host.
The fungal growth of the 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 fungus then 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.
The fungus will grow anywhere that woolly aphid honeydew is deposited which may present a diagnostic challenge. It is common for thick fungal accretions to 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. 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.