Does Redberry Mite affect only blackberry species?
Thank you for your question. First, here is an Extension article (https://pnwhandbooks.org/insect/small-fruit/cane-fruit/cane-fruit-redberry-mite) about the mite itself (Acalitus essigi), explaining what it is and treatment recommendations.
Second, eriophyid mites consist of more than 200 genera, Acalitus essigi being just one. And they tend to infect specific species of plants, as explained in this article: http://oregonstate.edu/dept/nurspest/eriophyid_mites.htm
Hope this is helpful.