The Warblers and The Aphids

Top Photo: Northern Parula on river birch.

The other day while down in Explore the Wild on a cool October morning there was an active group of migrant songbirds working the trees along the shoreline. The group was composed of mostly yellow-rumped warblers, a few northern parulas and some kinglets. While the yellow-rumped warblers (butter-butts) were attracted to the wax myrtle fruit, which is in abundance this year, a river birch tree held the attention of the other birds in attendance.

Yellow-rumped warbler (butter-butt) on its favorite winter food, wax myrtle fruit.

What was it about this river birch that demanded these birds’ scrutiny. The warblers and kinglets were making hay attacking the undersides of the birch leaves. I had to have a closer look.

N. parula inspecting the undersides of the birch leaves.

Turning over one of the leaves revealed what all of the excitement was about. Insects in the form of aphids were on the undersides of the leaves. Nearly every leaf I turned over had tiny aphids clinging to its underside. This is what the hungry migrants were doing, feeding on aphids.

Aphids cover the bottom side of the birch leaves.

I could see at least two different kinds of aphids. Both adults and nymphs of a species in the genus Calaphis was represented, and another species of aphid which spends part of its life cycle on witch hazel and part of its life on birch was also there. The former apparently spends its entire life cycle on birch. If you look carefully at the enlarged photo below you may see two adults and one transparent nymph between them.

Yellowish adult and transparent nymph between them, and aleurodifrom of whitchhazel leaf gall aphid (top left).

The other aphid species can also be seen in this photo (above), specifically in the top left corner. It’s the roundish black object with white fringe both around its body and its center. This aphid is called the witchhazel leaf gall aphid and as seen in the photo is in the aleurodiform stage of its life.

Witchhazel leaf gall aphids give birth to nymphs which later develop wings and fly off to witch hazel. They then give birth to wingless males and females who lay eggs that overwinter on the plant. The following spring when the eggs hatch the young aphids induce the leaves of the witch hazel to form galls, (similar to the one pictured). The aphids feed within the gall and in late spring or early summer mature and fly off to birch trees, bare offspring, and then feed on the birch’s leaves.

A cone gall.

It’s all connected.

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