I've not heard or read of any evidence to support the notion that beneficial nematodes have any impact on the control of narcissus bulb fly. The bulb fly larvae inhabit and feed on the bulb while the nematodes are soil dwellers - it's hard to see how their paths would easily cross. And since the nematodes are a rather pricey approach, I might consider other options first before entering to what might be at best just an expensive experiment:-)

I've attached a link from one of our local extension services that addresses this problem. It might be helpful.

Here is a link that might be useful: Narcissus bulb fly

I read something about it -- the idea is that the larvae travel from the soil surface down to the bulb and the nematodes will intercept them when they try to travel to the bulbs.

From what I've read it's pretty predictable time of year in spring when the narcissus bulb fly lays eggs and the larvae travel down to the bulbs so if the nematodes are released prior to this sounds to me like a good plan.

actually one posting I read said predictably May 1 but that was in Indiana, anyone know when the narcissus bulb flys lay their eggs in the Pacific Northwest?

I'm sorry but I still have serious reservations on the effectiveness of using nematodes. First, the larvae are generally nowhere near the soil. The adult fly lays eggs deep into the bulb foliage, sometimes actually tunneling under the paper sheath of the bulb itself to deposit her eggs. They hatch and the maggots immediately start working their way into the bulb itself, where they remain over winter. It is not until they begin to pupate in early spring that they move into the soil and by then it is far too late for nematodes to be of any value.

Beneficial nematodes need warm soil temperatures to regenerate and start feeding, usually around 50F. This generally does not occur in the Puget Sound area until late May, so the timing of this control may be off slightly as well as questions about its effectiveness. And at $20 something a pop for the nematodes, it is kind of an expensive proposition that may or may not have any benefit. Again, after more than 30 minutes of online research, I didn't turn up a single hit that posed nematodes as a control agent for this problem.

FWIW, the flies are typically present in this area in late spring. Promptly removing the dried, spent foliage, especially of early blooming narcissus, should go a long way to control bulb fly damage.

This sounds horrible. I would hate to lose mine. How common of a problem is it? I thought iris borers were bad, I didn't know daffodils HAD any pests.