|D. antiqua larvae feeding on Allium porrum|
Hylemya antiqua Meigen, 1826
Morphology and biology
The onion fly has an ash-grey body and resembles a housefly. The male has a longitudinal stripe on the abdomen which is lacking in the female. The legs are black, the wings transparent, and the compound eyes brown. The eggs are white and elongated and are laid in groups on the shoots, leaves and bulbs of host plants and on the ground nearby. The larvae are white and cylindrical and hatch in three to eight days. Each batch of larvae tends to keep together and collectively create large cavities in bulbs. More than fifty maggots may feed on one bulb, sometimes originating from eggs laid by several females. The larvae moult three times, feed for about twenty days, and grow to about one centimetre long. The pupa is brown, ringed and ovoid and measures 7 millimetres (0.28 in) long. Pupation occurs in the ground with the pupal phase from the spring generation lasting two or three weeks. Late generation pupae overwinter in the soil.
The onion fly is found in North America, Western Europe, Russia, Central Asia, China, Japan and Korea but is absent from deserts. In the far north of its range it has one generation per year, but further south there may be two, three or four generations in one year.
The larvae damage bulb onions, garlic, chives, shallots, leeks and the bulbs of flowering plants. The first generation of larvae is the most harmful because it extends over a long period owing to the females' longevity and occurs when the host plants are small. Seedlings of onion and leek can be severely affected as can thinned-out onions and shallots. Less damage occurs in wet and cold springs as this delays the development of the larvae. When plants are attacked, the leaves start to turn yellow and the bulbs rot quickly, especially in damp conditions. Control measures include crop rotation, the use of seed dressings, early sowing or planting, survey and removal of infested plants, and autumn digging of the ground to destroy the pupae.
- Harris, M; Miller, J (1988). "Host-acceptance behaviour in an herbivorous fly, Delia antiqua". Journal of Insect Physiology 34 (3): 179–90. doi:10.1016/0022-1910(88)90048-0.
- Harris, Marion O.; Miller, James R. (July 1983). "Color Stimuli and Oviposition Behavior of the Onion Fly, Delia antiqua (Meigen) (Diptera: Anthomyiidae)". Annals of the Entomological Society of America 76 (4): 766–71.