''Delia antiqua'', commonly known as the onion fly, is a

cosmopolitan Cosmopolitan may refer to: Internationalism * World citizen, one who eschews traditional geopolitical divisions derived from national citizenship * Cosmopolitanism, the idea that all of humanity belongs to a single moral community * Cosmopolitan ...

pest of

crops A crop is a plant that can be grown and harvested extensively for profit or subsistence. In other words, a crop is a plant or plant product that is grown for a specific purpose such as food, fibre, or fuel. When plants of the same species a ...

. The

larvae A larva (; : larvae ) is a distinct juvenile form many animals undergo before metamorphosis into their next life stage. Animals with indirect developmental biology, development such as insects, some arachnids, amphibians, or cnidarians typical ...

maggot A maggot is the larva of a fly (order Diptera); it is applied in particular to the larvae of Brachycera flies, such as houseflies, cheese flies, hoverflies, and blowflies, rather than larvae of the Nematocera, such as mosquitoes and cr ...

s feed on

onion An onion (''Allium cepa'' , from Latin ), also known as the bulb onion or common onion, is a vegetable that is the most widely cultivated species of the genus '' Allium''. The shallot is a botanical variety of the onion which was classifie ...

garlic Garlic (''Allium sativum'') is a species of bulbous flowering plants in the genus '' Allium''. Its close relatives include the onion, shallot, leek, chives, Welsh onion, and Chinese onion. Garlic is native to central and south Asia, str ...

, and other

bulb In botany, a bulb is a short underground stem with fleshy leaves or leaf basesBell, A.D. 1997. ''Plant form: an illustrated guide to flowering plant morphology''. Oxford University Press, Oxford, U.K. that function as food storage organs duri ...

ous plants.

Morphology and biology

The onion fly has an ash-grey body and resembles a

housefly The housefly (''Musca domestica'') is a fly of the suborder Cyclorrhapha. It possibly originated in the Middle East, and Cosmopolitan distribution, spread around the world as a commensal of humans. Adults are gray to black, with four dark, lo ...

. 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 An egg is an organic vessel in which an embryo begins to develop. Egg, EGG or eggs may also refer to: Biology * Egg cell, the female reproductive cell (gamete) in oogamous organisms Food * Eggs as food Places * Egg, Austria * Egg, Switzerland ...

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 3 to 8 days. Each batch of larvae tends to keep together and collectively create large cavities in bulbs. More than 50 maggots may feed on one bulb, sometimes originating from eggs laid by several females. The larvae moult three times, feed for about 20 days, and grow to about 1.0 cm long. The pupa is brown, ringed, and ovoid and measures long.

Pupa A pupa (; : pupae) is the life stage of some insects undergoing transformation between immature and mature stages. Insects that go through a pupal stage are holometabolous: they go through four distinct stages in their life cycle, the stages th ...

tion occurs in the ground with the pupal phase from the spring generation lasting two or three weeks. Late-generation pupae overwinter in the soil.

Distribution

The onion fly is found in

North America North America is a continent in the Northern Hemisphere, Northern and Western Hemisphere, Western hemispheres. North America is bordered to the north by the Arctic Ocean, to the east by the Atlantic Ocean, to the southeast by South Ameri ...

Western Europe Western Europe is the western region of Europe. The region's extent varies depending on context. The concept of "the West" appeared in Europe in juxtaposition to "the East" and originally applied to the Western half of the ancient Mediterranean ...

Russia Russia, or the Russian Federation, is a country spanning Eastern Europe and North Asia. It is the list of countries and dependencies by area, largest country in the world, and extends across Time in Russia, eleven time zones, sharing Borders ...

Central Asia Central Asia is a region of Asia consisting of Kazakhstan, Kyrgyzstan, Tajikistan, Turkmenistan, and Uzbekistan. The countries as a group are also colloquially referred to as the "-stans" as all have names ending with the Persian language, Pers ...

China China, officially the People's Republic of China (PRC), is a country in East Asia. With population of China, a population exceeding 1.4 billion, it is the list of countries by population (United Nations), second-most populous country after ...

Japan Japan is an island country in East Asia. Located in the Pacific Ocean off the northeast coast of the Asia, Asian mainland, it is bordered on the west by the Sea of Japan and extends from the Sea of Okhotsk in the north to the East China Sea ...

, and

Korea Korea is a peninsular region in East Asia consisting of the Korean Peninsula, Jeju Island, and smaller islands. Since the end of World War II in 1945, it has been politically Division of Korea, divided at or near the 38th parallel north, 3 ...

, but is absent from deserts. In the far north of its range, it has one generation per year, but further south, two, three, or four generations may occur in one year.

Economic significance

The larvae damage bulbs of onions,

chives Chives, scientific name ''Allium schoenoprasum'', is a species of flowering plant in the family Amaryllidaceae. A perennial plant, ''A. schoenoprasum'' is widespread in nature across much of Eurasia and North America. It is the only spe ...

shallot The shallot is a cultivar group of the onion. Until 2010, the (French red) shallot was classified as a separate species, ''Allium ascalonicum''. The taxon was synonymized with '' Allium cepa'' (the common onion) in 2010, as the difference was t ...

leek A leek is a vegetable, a cultivar of ''Allium ampeloprasum'', the broadleaf wild leek (synonym (taxonomy), syn. ''Allium porrum''). The edible part of the plant is a bundle of Leaf sheath, leaf sheaths that is sometimes erroneously called a "s ...

s, and 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.

Morphology and biology

Distribution

Economic significance

References

Further reading