Cottonwood Gall Aphids (Pemphigus populitranversus)

Pemphigus popilitranversus

Cottonwood Gall

While I was raking leaves off our small “lawn,” my wife (knowing full well the answer would be yes) asked me if I wanted to see a leaf gall. It was formed on the petiole of an Eastern Cottonwood (Populus deltoides). I checked and identified that a Cottonwood Gall Aphid caused the gall.  Poplar Petiole Gall Aphid is another common name for this species.

Pemphigus popilitranversus

Cottonwood Gall                  Left hand gall showing transverse split

It is a hollow gall, not quite round, with a transverse split. It occurs along the petiole (the stem of a leaf) just below the blade. I cut a few open and found a waxy substance but no insects. They might have exited through the slit. I opened one more and found the adult aphid.

Pemphigus popilitranversus

Interior of Cottonwood Gall    L – shed skin                 R – adult winged aphid

I Googled the scientific name and the phrase “life cycle” and found Roberta Gibson’s informative and fun blog “Growing with Science (The Poplar Petiole Gall Aphid was the “Bug of the Week” in May of 2015.) She explains the aphid’s life cycle. Aphids seldom have straight forward life cycles. They over winter as eggs on Cottonwood twigs. They hatch in the spring and feed on the leaf petioles, causing the plant to produce the gall. Then the insect moves inside. It becomes a winged adult and exits through the slot in the gall’s side. They complete their life cycle on the roots of cabbage, turnips, or another member of the mustard family (Brassicaceae). Another common name is Cabbage Root Aphid. The aphids complete their life cycle by flying back to Cottonwoods and depositing eggs on the twigs or bark.

This is a great time of year to look for galls. Get outside and enjoy Nature. Also, check out Roberta’s blog and website. Even though she is based out of Arizona many things she writes about occur in Michigan.
Copyright 2016 by Donald Drife

Webpage Michigan Nature Guy
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Alternate Budded Trees with True Terminal Buds II

Populus deltoides

Eastern Cottonwood

Eastern Cottonwood (Populus deltoides) has large (1-2 cm long) terminal buds that are shiny and sticky. The leaf scars have three bundle scars. The pith has a star-shaped cross section.

Populus balsamifera P. deltoides

L – R Balsam Poplar, Cottonwood leaf buds, Cottonwood flower buds





Balsam Poplar (Populus balsamifera) is similar to Eastern Cottonwood but with very aromatic buds. The leaf scars have three to five bundle scars. Eastern Cottonwood is primarily a southern species and Balsam Poplar is northern.


Populus grandidentata, Bigtooth Aspen

Bigtooth Aspen


Bigtooth Aspen (Populus grandidentata) has a terminal bud less than 1cm long. The center of the scale is covered with short dense gray hairs. The lateral buds diverge from the stout twigs.



Populus tremuloides, Quaking Aspen

Quaking Aspen



Quaking Aspen (Populus tremuloides) is similar to Bigtooth Aspen. The terminal buds lack the gray hairs. The lateral buds are appressed to the thin twig.



L-R Prunus serotina, P. virginiana

L-R Black Cherry, Choke Cherry

Black Cherry (Prunus serotina) has a blunt terminal bud. The bud scales are reddish-brown. The lateral buds are appressed. The bark is black with rounded plates giving it a “burnt potato chip” look.

Choke Cherry (Prunus virginiana) has a terminal bud that is longer and more pointed than a Black Cherry’s. The lateral buds are more or less divergent. The brown bud scales have a two-tone look.

Quercus Oaks



Oaks (Quercus spp.) have buds clustered at the ends of their twigs. The species are often difficult to distinguish.



Copyright 2013 by Donald Drife

Webpage Michigan Nature Guy
Follow MichiganNatureGuy on Facebook