Thanks, yardn_gardn! I was wondering about BTi. I have some mosquito dunks, which I've also used for fungus gnats - thought I might crumble one and bury a few bits around these guys just in case. It might help, and can only hurt flies so.... (I'm not too knowledgeable about flies, but I don't think this small patch would have an effect on the whole garden community anyway).
These shallot seeds came from shallots someone grew from McKenzie bulbs, and sent in to Nicky's swap. I'm pretty excited about how hardy they are.
I would certainly have spaced them more generously if I had more space or they were a bit less abundant. So hopefully I will get some bulbs to replant, and maybe the spacing will work next time... one thing for sure, the "multiplier" gene is pretty powerful in this lot.