Lesser bulb fly (Eumerus tuberculatus)
Narcissus bulb fly (Merodon equestis)
Pest description and damage The adult narcissus bulb fly is about 0.5 inch long and closely resembles a small bumblebee; it can be recognized by its aggressive behavior of bumping into other bees and female bulb flies. The larva is a fat, yellowish-white, wrinkled maggot about 0.75 inch long. The lesser bulb fly adults are blackish green with white markings on the abdomen; the larvae are smaller and more numerous in the bulbs. The maggots of the narcissus bulb fly burrow into the bulbs near the basal plate and feed inside the bulbs, destroying bulb scale and flower parts while maggots of the lesser bulb fly are thought to be scavengers. Infested bulbs may develop a few, grassy-looking leaves if the bulb is not too badly damaged. Severely damaged bulbs are soft, brown, and decayed. The narcissus bulb fly attacks amaryllis, galtonia, hyacinth, iris, lily, leucojum, narcissus, scilla, tulip, and vallota. The lesser bulb fly also attacks and may be a primary pest on onions and shallots and other bulbs.
Biology and life history The life history of the two pests are similar. The females lay eggs near the bulbs during May or early June. The eggs hatch into grubs that move down into the soil and burrow into the base of the bulb to feed there, reducing the bulb's center to a rotten mass. In the process, the embryonic flowers that would have unfolded the following spring are destroyed. After feeding, larvae pupate in the bulb or soil. In the spring, they emerge as adult flies to mate and lay eggs. Lesser bulb fly may have a second generation.
Pest monitoring Check daffodil plantings for spindly, grassy leaves and no flower. Dig up bulbs to inspect for hollowed out bulbs, decay followed by scavengers such as millipedes and sowbugs.
Narcissus fly can be evaded by deep planting (10 inches). Plant in open areas exposed to wind. Bulb flies are usually less of a problem in such sites. Covering foliage of plants with a row cover after bloom prevents egg-laying. Plant only firm, healthy daffodil bulbs. Soft bulbs may be infested from the previous season. Destroy any soft bulbs to prevent emergence of adult bulb flies. Dig and store bulbs after foliage dries to prevent the bulb fly from laying eggs. A hot water bath has also been found to be effective in killing maggots in infested bulbs. Maggots can be killed if bulbs are submerged in water kept at about 110°F for 40 minutes. Care must be taken to avoid overheating the bulbs even for a short time as the bulbs may be adversely affected by high temperatures.
For more information
Anon. Narcissus bulb fly (http://ipm.ncsu.edu/AG136/fly4.html)
Gill, S. 2010. Narcissus bulb fly. TPM/IPM Weekly Report for Arborists, Landscape Managers & Nursery Managers (http://ipmnet.umd.edu/landscape/lndscpalerts/2010/10apr16l.pdf)