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On May 18, 2007, Illoquin from Indianapolis, IN (Zone 5b) wrote:
aka Lampetia equestris
These are visible and audible here the 1st of May, like clockwork. They fly & mate and lay eggs for another 3 or 4 weeks, depending on the weather. They can always be found in the sun, even if it is just a teeny patch in the woods.
It has one set of wings, and though it looks like a honeybee or bumble bee, it is truly a fly.
The bulb fly deposits eggs at the base of daffodil foliage and after 10-15 days, the eggs hatch & the larva follow the foliage down to the bulb where is spends the summer and fall munching on the daffodil bulb. Each female lays about 40 eggs. Each maggot will eat everything he can easily get to, so if bulbs are very close together underground, he will eat many. The bulbs will be ruined, if not outright killed, the only sign that they have been there is the teeny tiny little foliage that comes up the following spring from what the grubs leave behind of the basal plate.
Commercial growers harvest bulbs and give Narcissus bulbs a hot water treatment before shipping, but the homeowner could go with an organic drench made from pyrethrins and canola oil while the bulbs are in the ground. It would be applied 3 or 4 times to the base of the foliage once the bulb fly is seen. (Poured on with a watering can once a week for 4 weeks.)
Imidacloroprid, a granular insecticide which is not labeled for the control of narcissus Bulb Fly, is another possibility. At the rate of 2-3 ounces/100 squre feet and either hoed or watered into the soil, it is used by some growers with large collections.
If you try to erradicate this bulb fly, you also must spray/drench bulbs like allium, amaryllis and ornithogalum.