The one thing I do to avoid them is to always move my perennial multiplying onions in summer, when they are through making tops. I cure out the roots (there are little shallots down there) and gather up the bulblets, which I replant in a fresh spot in early fall.

When I have left perennial onions in the same place for a year, they attract root maggots with their rotting tissues. I've never seen root maggots on weed-onion roots, and I've pulled thousands.

The rule is to always rotate onions each year. Diazanon used to do the trick, but it's not even available any more.

Well, onions never go in the same spot twice here, but it's not a half-mile rotation (as recommended by one of the sites I visited) by any stretch. I find them most in my garlic, which is fall planted. The original clove seems to break down over the winter as the inner shoot grows and I wonder if that is attracting them. There aren't so many dying garlics this year as last, and this is a much more normal spring so perhaps the problem is resloving itself.

About the wild onions, I don't know if they are a host, but one must exist somewhere in the wild because the adults can only fly about a mile. No one else near me is growing onions- corn, soy, wheat, rye yes, and lots of pasture and woods. Thanks for your input, it reaffirms what I am reading elsewhere. Cheers!