Woolly Alder Aphids (Prociphilus tessellatus, family Aphididae) produce large, white fluffy colonies on the branches of their namesake host making the branches look like they're covered in patches of white hair. A close look will reveal woolly aphid nymphs exuding strands of white waxy filaments from block-like structures on their backs (tessellatus means "mosaic pattern").
I've encountered these unusual woolly aphids twice over the past couple of weeks. My friend Ron Rothhaas (Arbor Doctor, LLC, Cincinnati, OH) gave me directions to heavy infestations on several alders used as street trees in Cincinnati. I also came across these fluff-covered aphids adorning alders in southern West Virginia.
Woolly alder aphids closely resemble Beech Blight Aphids (Grylloprociphilus imbricator) which are found exclusively on the twigs and branches of American beech (Fagus grandifolia). Indeed, both aphids belong to the same subfamily, Eriosomatinae (woolly and gall-making Aphids), and tribe, Pemphigini.
However, unlike their beech-sucking cousins, woolly alder aphids don't pulse their posterior ends in unison when they're disturbed. This unusual defense behavior is responsible for beech blight aphids being called "boogie-woogie aphids." More about these aphids later.
Woolly alder and beech blight aphids practice the same phloem-sucking behavior and both produce copious quantities of honeydew which becomes colonized by a specific sooty mold fungus, Scorias spongiosa (Ascomycete). The fungus has an obligate relationship with these and a few other woolly aphids.
The sooty mold fungus looks like other black sooty molds at the beginning. The mycelia form a dense, black, "fuzzy" mat on top of the honeydew.
However, over time, 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.
The spongy growths eventually harden and turn black in the fall. They remain evident throughout the winter and are sometimes mistaken for other tree maladies.
Woolly Alder Aphids or Maple Blight Aphids?
Woolly alder aphids have two trees hosts: alder and silver maple (Acer saccharinum). In fact, the alternate common name for this aphid is Maple Blight Aphid.
At this time of the year, some of the aphids on alder will mature into males and females with wings and fly to silver maple. Others remain on alder for the winter. Indeed, a portion of the colony will always stay on alder year-after-year; there is no requirement for the aphids to fly to silver maple to complete their life cycle.
The winged females lay eggs in bark crevices on silver maples; this is the overwintering stage. The eggs hatch in the spring and the resulting nymphs migrate to newly expanding maple leaves where they line-up on midveins and use their piercing-sucking mouthparts to tap into phloem vessels.
These aphids are all females and they reproduce asexually to form large, fluffy colonies. Heavy infestations can cause noticeable leaf curling and the colonies produce copious quantities of honeydew that rains down on leaves, branches, etc. to become colonized by black sooty molds
By mid-summer, the colonies of "maple blight aphids" produce adults with wings that fly to alders. These relatively large aphids are covered in waxy filaments and look like flying puffballs. They are not particularly good flyers and large numbers can make them a serious nuisance pest as they drift around landscapes with heavily infested maples.
None of the aphids remain on silver maples past mid-summer. This "disappearing act" can be very dramatic with high populations seeming to suddenly disappear as the fluffy winged adults leave the maples to seek alders.
Woolly alder aphids/maple blight aphids are mainly nuisance and aesthetic pests. They cause little damage to the overall health of their tree hosts so insecticide applications are seldom warranted. The aphids attract a wide range of predators and parasitoids that play a significant role in naturally regulating populations. Several of my images showed characteristic lacewing (family Chrysopidae) eggs laid near the aphids; harbingers of doom.
A Harvester of Woolly Aphids
A close look at woolly alder aphid colonies may reveal one of the most unusual caterpillars found in Ohio. The slug-like caterpillars of the Harvester Butterfly (Feniseca tarquinius, family Lycaenidae) are the only strictly meat-eating butterfly caterpillars found in the U.S. The butterfly species is also the only member of the monotypic genus Feniseca.
I was amazed to see the carnivorous caterpillars slinking among their woolly prey without producing any reaction from the aphids. The sheep-like aphids seemed totally unaware of the marauding wolves converting their sisters into watery, yellowish smears.
Harvester butterfly caterpillars commonly feed in groups (wolfpacks?) and apparently confine their feeding to woolly aphids. You may also find the caterpillars creeping among colonies of other woolly aphids such as Woolly Elm Aphids (Eriosoma americanum). The adult butterflies may be spotted fluttering in close proximity to their woolly caterpillar food.
However, the harvester butterfly does not seem to hunt beech blight aphids. Research has shown that the nymphs are highly aggressive against predators. If the organized boogie-woogie doesn't work, the nymphs will mass-attack using their piercing-sucking mouthparts to inflict serious damage to predators; possibly including harvester caterpillars. Perhaps the aphid's gyrations are actually a war dance!
You can read more about this unusual aphid behavior by clicking on this hotlink that takes you to a Scientific American article titled, "Dancing woolly aphids will probably stab you":