I posted this on the veggie forum, before I found out there was an allium forum, so I'm posted it here too..
I found this on one of my scallion leaves/stem. Any idea what it is?
I think that is a cluster of pupae of onion root maggots. I would put the leaf in a jar and keep it in the shade. Hairy little flies will emerge within a week. Then put the jar in the sun to kill them.
It's a good image! Today I plan to scout my scallions and leeks to see if I can find somethings similar. The scallions in particular are not looking so hot, and I had a lot of root maggots in my red shallots this year.