Carrot Fly living in soil over winter?

I got carrot fly in a half-barrel of carrots last season.

Dare I use the soil from the barrel this season in a parsnip trench, as it is a nice light, sandy mixture, or could it have fly larvae in it? Reading up suggests over-wintering by fly and then they "emerge from the soil"...

If I do use it, I don't want fly emerging from the soil UNDERNEATH this years purchased Environmesh...would rather defeat the object...

Should I bin, treat or what?...

Phill