Narcissus bulb fly—Merodon equestris
Lesser bulb flies—Eumerus spp.
Adult bulb flies are stocky, hairy flies, blackish to dark
green with pale yellow, orange, or gray markings. Adult
bulb flies look like small bumble bees and may also resemble
other beneficial species. On warm sunny days, adults
often hover around blooming plants, where they feed on pollen
and nectar. Bulb fly larvae are plump, wrinkled, dirty
yellow, gray, white, or brownish maggots with a short brown
or blackish breathing tube at their rear. Maggots of several
species of flies infest bulbs of all types, including daffodil,
iris, lily, and tulip.
The adult lays an egg in spring or summer on exposed bulbs or stems at or near the base of plants. After 5 to 14 days, the egg hatches and a larva wriggles down into the soil or moves down along the outside of the bulb. It feeds on the bottom of the bulb where the roots emerge then enters and feeds inside the bulb. The larva develops through three instars over a period of 9 to 10 months. In spring the larva pupates in a brownish case inside the bulb, or it emerges and pupates nearby in topsoil. Pupation takes 4 to 8 weeks, after which the adult emerges, mates, and females lay eggs. Adults live about 2 to 3 weeks.
Larvae feed in bulbs, causing yellow foliage and stunted plants. If infested, large bulbs produce fewer leaves and distorted growth. Instead of a large shoot, small leaves may emerge in a ring around the central growing point that has been killed by a larva. Blooms and small bulbs often die. Narcissus bulb fly attacks healthy plants; lesser bulb flies prefer bulbs and rootstocks that are already diseased or decayed.
Prevention is the most effective bulb fly
control strategy. Purchase and plant only pest-free
bulbs. Handle bulbs carefully to avoid injury. Remove
and destroy infested bulbs and plants as soon as you find
Bulb fly life cycle (by Valerie Winemiller, adult from C.F. Doucette. 1959. The Narcissus Bulb Fly. USDA Leaflet 444.)