Delia (fly)


The genus Delia is part of the fly family Anthomyiidae.
The genus Delia contains approximately 300–340 species worldwide. At present about 170 species are recorded from the Palaearctic region, and 162 species from the Nearctic region, 44 of which are Holarctic. Afrotropical fauna includes 20 Delia species. Griffiths described 49 new species in his recent revision of the Nearctic species, nearly a third of the present Nearctic total, and similar intensive revisions in other parts of the world are expected to produce many more, especially in the Middle East, mountainous regions of Central Asia, Nepal, and Mongolia.

Biology

Several important agricultural pests are Delia species, including D. radicum, the cabbage maggot, D. floralis, the turnip maggot, and D. antiqua, the onion maggot. The larvae of these flies, which tunnel into roots and stems of host plants, can cause considerable agricultural yield losses. Although most members of this genus have larvae that feed on stems, flowers, and fruits of plants, a few others have larvae that are leaf miners. The larvae of Afrotropical Delia species are mainly phytophagous, and have been found in various cereal crops and grasses, including Cynodon, Secale, Hordeum, Setaria, Pennisetum, Chloris, Sorghum, and Eleusine species.
The cabbage maggot has been successfully reared in colonies for research purposes.
Delia rely on a number of factors to identify their respective hosts. Chief among these is scent. D. radicum, for example, is especially sensitive to isothyocyanates to recognize cabbage plants. In addition, colour, position, and visual prominence of the flower provide cues to the fly. D. radicum recognizes the yellow colour and round shape of its host, thus preferring large, circular discs close to the ground over smaller discs higher up. Another species where host identification was studied is D. antiqua. This onion fly prefers to lay eggs when exposed to dipropyl disulphide, and reduced egg deposition if the host flower shape and colour were modified.

Species