The Society for the study of flies (Diptera)

I have been working a local 1k square this year in which i couldn't find any Ramsons. I was somewhat taken aback this lunchtime when I visited a sunny corner of the woods to find it swarming with Portevinia. The area does have a lot of Sand Leek (Allium scorodoprasum) in it. Is this a known host of Portevinia?

I'll revisit the area to search at greater length but I would have thought a stand of Ramsons should be pretty obvious. The flies were easily into double-figures.

Cheers
Ali