Pink and white patches on maple leaves – Erineum mites
Sam was looking at one of our maple trees on May 29, 2021, and noticed that there were glittery patches on many of the leaves. Some of the patches were pink,
and some were white.
She noted that they looked a lot like spots of glitter nail polish. So, I ran up the magnification to see what the patches looked like in more detail:
Now we are starting to see some structure, they appear to be sheets of either transparent or reflective spheres. Looking at the pink ones a bit closer,
we see that the spheres vary in size, and may be embedded in a mass that is probably the solids from evaporated sap. The fact that the spheres are not all the same size suggests that they are not eggs. Interestingly, we can also see that some of them are pink and others are not, which is weird if they are all caused by the same organism.
So, looking up “pink patches on maple leaves”, I find that these are probably “erineum patches”, produced by mites in the family Eriophyidae. Unfortuately, I can’t find any pictures of the erineum patches at high magnification, so I can’t confirm that they have this iridescent spherical structure. Also, I don’t know whether the spheres are actually the mites themselves, or whether they are galls forming on the leaf surface with the mites inside.
Anyway, these are apparently classified as a type of gall, even though it is more of a sheet than a bulgy growth like we normally associate with galls. They don’t actually do any significant harm to the tree, although they can be a bit unsightly if the infestation gets really severe.
I don’t know why some of them are pink and others are clear. Maybe they are two different species of mite, one of which is pigmented and the other is not. Or maybe some parts of the leaf just secrete colored compounds into galls, while other parts do not. But anyway, even though these do not at first appear to be arthropods, they actually are. Or, at least, they are caused by arthropods.
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Great photography, as usual. It would be interesting to put a sample under a microscope and see if the bug was there. I’d guess that it was, otherwise the mite would have had to bite the plant, get coated in goo and then crawl off.
Or is that what they do?