Delia floralis, commonly known as the turnip root fly or summer cabbage fly, is a cosmopolitan pest of crops

Crop (agriculture)

A crop is a non-animal species or variety that is grown to be harvested as food, livestock fodder, fuel or for any other economic purpose. Major world crops include maize , wheat, rice, soybeans, hay, potatoes and cotton. While the term "crop" most commonly refers to plants, it can also include...

. The larvae

Larvae

In Roman mythology, lemures were shades or spirits of the restless or malignant dead, and are probably cognate with an extended sense of larvae as disturbing or frightening...

 or maggots feed on the roots of various plants in the Brassicaceae

Brassicaceae

Brassicaceae, a medium sized and economically important family of flowering plants , are informally known as the mustards, mustard flowers, the crucifers or the cabbage family....

 family.

Morphology and biology

This species resembles the closely related cabbage root fly in appearance though it is slightly larger at seven to eight millimetres long. The body is light gray and the yellowish wings are transparent with yellow veins. Over most of its range, there is only one generation of this fly each year. The eggs

Egg (biology)

An egg is an organic vessel in which an embryo first begins to develop. In most birds, reptiles, insects, molluscs, fish, and monotremes, an egg is the zygote, resulting from fertilization of the ovum, which is expelled from the body and permitted to develop outside the body until the developing...

 are laid seven to ten days after the adult has emerged from the pupa

Pupa

A pupa is the life stage of some insects undergoing transformation. The pupal stage is found only in holometabolous insects, those that undergo a complete metamorphosis, going through four life stages; embryo, larva, pupa and imago...

. They are white and cigar-shaped and are laid in groups of thirty or forty eggs at the root collar of the host plant or on the ground nearby. Often several females lay eggs on one plant. The glossy white or yellow larvae hatch in five to fourteen days. They feed for about forty days, moulting three times, eating the young roots or tunneling into the main root of the host plant or even penetrating into the basal part of the leaves of hearting cabbage. The pupae are brown and about six millimetres in length. The insect overwinters as a pupa in the ground at a depth of five centimetres or more. The pupae can endure frosts of -33°C and in the following year the adults emerge at varying dates, doing so when the soil temperature reaches 18°C at the depth of the pupae.

Distribution

The turnip root fly is found in Western Europe

Western Europe

Western Europe is a loose term for the collection of countries in the western most region of the European continents, though this definition is context-dependent and carries cultural and political connotations. One definition describes Western Europe as a geographic entity—the region lying in the...

, Russia

Russia

Russia or , officially known as both Russia and the Russian Federation , is a country in northern Eurasia. It is a federal semi-presidential republic, comprising 83 federal subjects...

, Northeast China

Northeast China

Northeast China, historically known in English as Manchuria, is a geographical region of China, consisting of the three provinces of Liaoning, Jilin and Heilongjiang. The region is sometimes called the Three Northeast Provinces...

, Korea

Korea

Korea ) is an East Asian geographic region that is currently divided into two separate sovereign states — North Korea and South Korea. Located on the Korean Peninsula, Korea is bordered by the People's Republic of China to the northwest, Russia to the northeast, and is separated from Japan to the...

, Japan

Japan

Japan is an island nation in East Asia. Located in the Pacific Ocean, it lies to the east of the Sea of Japan, China, North Korea, South Korea and Russia, stretching from the Sea of Okhotsk in the north to the East China Sea and Taiwan in the south...

 and North America

North America

North America is a continent wholly within the Northern Hemisphere and almost wholly within the Western Hemisphere. It is also considered a northern subcontinent of the Americas...

.

Economic significance

The larvae damage the roots of cabbage, turnip, radish, swede and other cruciferous crops. The growth of damaged plants is slow and development is poor resulting in a reduced yield. Large scale attacks cause cessation of growth with the plants exhibiting a leaden hue and wilting, subsequently turning yellow and dying. Control measures include the early planting of strong plants, the use of peat-compost pots, the use of additional fertilizer, deep autumn ploughing after the harvesting of cruciferous crops and insecticide treatments.

Research

• A study made in 1993 investigated the behavioural and neural mechanisms involved in the oviposition behaviour of the turnip root fly.
• A study made in 2002 investigated the mortality rates of the eggs and larvae of the turnip root fly when treated with an insect pathogenic hyphomycetous fungus.
• A study made in 2008 investigated the combined effect of intercropping and attack by turnip root fly larvae on the level of glucosinolates in the host plant.