About Narcissus bulb fly
Narcissus bulb fly is a pest of Narcissus but may also attack Cooperia (evening rain lily), Galanthus (snow drops), Galtonia (summer hyacinth), Habranthus, Hymenocallis (spider lily), Leucojum (snowflakes), Pancratium, Sprekelia (Aztec lilies), Zephyranthes (rain lily), and Cipollini.
The adult is a large, hairy yellow and black fly. It resembles a small bumble bee. The female lays eggs on or near the crowns of narcissus or other hosts. Usually, only one larva will develop in each bulb. The larva is plump, white to yellow, wrinkled and ½ to ¾ of an inch long. As a result of the feeding, the bulb is reduced to a soft brown mass. Infested plants have yellow, stunted foliage or very little growth and the bulbs will feel spongy.
Full grown larva in damaged daffodil bulb. Photo: Whitney Cranshaw, Colorado State University, Bugwood.org
Management
To manage this pest in the home garden, discard all bulbs that feel spongy or are rotting.