During ‘Episode 10 - Witch Hazel Rising: An Explosive Late Bloomer’ we found a bunch of conical galls growing on the Witch-hazel leaves. These structures are created by Cone Gall Aphids (Hormaphis hamamelidis) and have a fascinating life. Each year, this Aphid goes through seven generations between spring and fall and only a couple are actually found on Witch Hazel.
The 1st generation, also known as “the gall makers” or “the stem mothers”, are all-female and hatch from “winter eggs” on witch-hazel branches. When the leaves emerge, they start depositing their eggs into the undersides of the leaf. When the first generation is done depositing eggs, they shrivel and die. The galls start forming in April and are fully developed by the end of May. Although many of the galls we saw in September looked fresh, they had actually been empty since before June.
At this point, the winged 2nd generation emerge and migrate to river birch trees (betula nigra). These ladies deposit about 50 larvae on the underside of birch leaves during the next week or so. When they’re all out of eggs, they shrivel and die.
The 3rd, 4th, and 5th all-female generations live on beach leaves and are also known as the 1st, 2nd, and 3rd Aleurodiform stages. These generations mimic whiteflies in the family Aleyrodidae (Aleurodiform means whitefly-shaped).
The 5th generation (or 3rd Aleurodiform stage) produces the 6th generation, also known as “the return migrants”. These winged ladies migrate to witch-hazel trees between August and early October. They deposit larvae on the bottom of the leaves, shrivel, and die.
The 6th generation is known as “the sexual generation” and for good reason. This is the only generation in the year with females and males. It is finally the time for sexual reproduction, proving for some genetic variation in the offspring. Mating is short-lived and the females deposit “winter eggs” on the branches and twigs of witch-hazel. These eggs survive the winter, hatch in the spring, and the cycle starts over.
Newer research revealed that Cone Gall Aphids at higher elevations go through as few as three generations in a year. It’s also important to note that each generation had many stages to pass through before adulthood. On average, each generation passed through 5 life stages in under 20 days! I wish we knew about this when we recorded the episode, but it’s not too late. If you’re determined (and/or lucky) you could find yourself some 6th generation Cone Gall Aphids right now. Good Luck!
1. Pergande, Theodore. The life history of two species of plant-lice inhabiting both the witch-hazel and birch. No. 9. US Government Printing Office, 1901.
FREE ONLINE: https://play.google.com/store/books/details?id=sdQaAAAAYAAJ&rdid=book-sdQaAAAAYAAJ&rdot=1
2. Von Dohlen, C. D., and D. E. Gill. "Geographic variation and evolution in the life cycle of the witch-hazel leaf gall aphid, Hormaphis hamamelidis."Oecologia 78.2 (1989): 165-175.
Reinstein Woods (Late September, 2016)