cockscomb gall

Look closely at the leaves of slippery elm (= red elm) (Ulmus rubra); you may be lucky enough to spot the unusual looking elm cockscomb galls produced by the so-called elm cockscomb aphid, Colopha ulmicola.  Although these galls are commonly mentioned in the literature, I've rarely seen them in southwest Ohio where elm sack galls produced by the aphid, Tetraneura ulmi, are the dominant aphid gall found on slippery elm.

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It is often said that a picture tells a thousand words. In this case, perhaps a few less, but it does tell multiple and layered stories. First, as shown by this image, one of the plant ID characteristics of elm (Ulmus) leaves is the uneven base to the leaf blade as shown here. This was the main point for the attendees at a recent Name That Tree program of OSU Extension at the OSU Mansfield campus. Secondly, of all the gall, the elm cockscomb gall insect (Colopha ulmicola) induced the DNA of this elm leaf to produce a proud new home for the insect’s progeny. Thirdly...