Poplar Petiole Gall Aphids
Continuing our August 12, 2012 bike ride, Sandy spotted a Balsam Poplar tree that was completely covered with these largeish galls. There was pretty much a gall for every leaf, and each gall was around a centimeter in diameter.
Splitting one of the galls open, we found that it was filled with these little aphids.
Some of the aphids were smaller and greenish, while others were larger, kind of a sooty-gray color, and had wings.
These are Poplar Petiole Gall Aphids, Pemphigus populitransversus. They pretty much exclusively infest poplar trees. I believe that they attach to the stem (petiole) of a new poplar leaf, and irritate it enough that it swells up to form a protective gall around them. The aphids can then hang out inside the galls, protected from the weather and from attack by predators, while feeding on the plant juices that weep out inside the gall.
The thing that was interesting was that, along the bike trail, Balsam Poplars were one of the most common types of trees, but there was only this single tree that had the gall aphids like that. It looks like there are susceptible and resistant trees, and when the aphids find a susceptible tree they exploit it like crazy.
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I’m guessing that tree was a poplar spot for the aphids.
Ba-da-bump!
I see similar galls on the cottonwood tree near our house. the gall is on the stem and when opened the aphids look very similar.
Very bad KTCat!
Fascinating life cycle.
Thanks for the photos & info on poplar aphids.