CAUTION: Taxon split. A 2023 paper by Miller et al. says T. glaucensis is "the only Tamalia aphid known to induce galls on A. glauca." See https://www.gallformers.org/gall/4937. In addition, galls on A. pringlei can be caused by either of two Tamalia species, so best ID is "Tamalia."

Separately, here are some tips for distinguishing Tamalia aphid galls and Exobasidium fungus galls on manzanita leaves. The two galls are surprisingly similar in appearance. Generally, however:
. Tamalia galls, like most insect galls, create enclosures.
. Tamalia galls usually occur on the leaf edge or along the leaf midrib.
. Tamalia galls are usually elongated.
. Exobasidium galls on manzanita leaves (EGAML) are often convex/concave blisters [E. arctostaphyli]; there is also an undescribed Exobasidium that turns the entire shoot tip red. Photographing both sides of the leaf will often show a smoothly concave area on one side.
. The red of EGAML is sometimes shiny, and the color often occurs on parts of the leaf that are not distorted.

Finally, additional information and a list of known hosts for Tamalia coweni can be found on InfluentialPoints.