We do not often see leafminers on magnolia, but the Plant and Insect Diagnostic Clinic received a sample that I suspect is damage is from the magnolia serpentine leafminer moth (Phyllocnistis magnoliella).
The caterpillar stage of this moth feeds close to the upper epidermis of the leaf and causes long, sort-of-silvery mines all over the leaf. They are not considered a pest of magnolia as usually it is only a few leaves that are affected.
Very little seems to be known about this moth's life-cycle. As with all leafminers control is not practical because the insect is protected within the leaf. If you notice them on your magnolia just enjoy the pretty winding lines on the leaves.
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