There's a company called, Greenlight Biosciences, that's developing an RNA-based pesticide for Varroa Mites. Last I spoke with the CEO, he mentioned positive results from trials.
https://www.greenlightbiosciences.com/in-the-pipeline-protec...
https://www.greenlightbiosciences.com/in-the-pipeline-protec...
Probably the better solution here is to stop trying to do industrial farming of bees, and move to a system where local populations of pollinators are cultivated and maintained year round. But sure, RNAi is probably better than the chemicals they're using now.