Cottony rosette stem galls on Wyoming big sagebrush

Here are photographs of a rosette gall that I'm trying to identify, all growing on Wyoming big sagebrush (Artemisia tridentata subs. wyomingensis at the Crooked River National Grassland in Madras, Oregon. Galls are between 1 and 4 cm in diameter and are composed of dozens of thin, pointed bracts coated with fine white hairs. There are thousands at the location.

I'm assuming they are some sort of Rhopalomyia (Cecidomiidae), but I can't find a good match in iNaturalist, BugGuide, or on any of the hundreds of web pages and books that document the various galls on sagebrush. Similar galls have also been observed by @ddubois2 on Artemisia cana in Montana (https://www.inaturalist.org/observations/45283788#activity_comment_4818259) and by @serpophaga on Artemisia dracunculus in California (https://www.inaturalist.org/observations/8919705, https://www.inaturalist.org/observations/8919707).

It seems improbable that something so striking is not yet described. If anyone has ideas on what it might be, I'd be grateful for any leads.

Julkaistu elokuu 3, 2020 12:00 IP. käyttäjältä colinpurrington