As students are currently flooding back onto campus and things are once again shifting into active term, your arboretum curator has taken the opportunity to remove branches and limbs from walking spaces. Living limbs, dead ones, branches covered in leaves, bare ones, and even the soft needles of cypress trees are being pruned away from the "head spaces" across the arboretum. While performing this seasonal maintenance near the Student Union Building, we noticed some rust-like growths in the pruned branches. Having struggled against cedar-apple rust (Gymnosporangium juniperii) for more than a decade, we are well-accustomed to unsightly rusts. But the simultaneous presence of white and purple growths on nearby branchlets made us do a double-take.
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| What is going on with these cypress leaves? The unexpected amount of color variation gave us pause and attracted our attention. |
These aren't rust at all! They're galls! Galls are growths created by tiny flies called cypress gall midges (Taxodiomyia sp.). These little critters are obligate parasites of the cypress, and the adult flies are terribly small. If you carefully dissected the large green-yellow gall on the right of the above photo, you could find tiny larvae crawling around in there, exerting chemical/enzymatic control over the tree. How odd!
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| Here we can see the life-cycle progress of gall-formation. They begin as white, budding, geometric-like structures seen on the left, which ripen into a frosty purple, pictured center. The galls then continue to mutate into more bulbous rusty lumps, like the one pictured on the right. These eventually fall from the tree and overwinter on the ground, finally releasing new midges during the following summer. |
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| Beginning stage of gall development |
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| Further development |
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| Toward the end of gall development |
See our previous post on this baldcypress from September 2019, which ends with a mention of this issue! Much water has passed under the bridge of life since then, but some things, including the Cecidomyiidae family of gall midges, never change.
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