Delia (=Hylemyia) antiqua (Meigen)
Common name: Onion maggot, onion fly.
Geographical distribution: North America, Western Europe and the Mediterranean region, Russia, Central and eastern Asia.
Morphology: The adult flies are grey-brown with dark stripes on the thorax, body length about 3-4 mm, wings transparent-yellow, antennae and leg dark. Abdomen yellow. Maggot about 7-8 mm long, whitish, the anterior end tapering.
Host plants: Onion, garlic, leek.
Life cycle: The pest may annually complete 2-5 overlapping generations, depending on the region. The adults live for about two months, feeding on nectar. Each female produces 50 to 200 eggs in batches which are placed on the shoots, leaves and bulbs of host plants and on the ground. The emerging maggots, which tend to stay together, excavate large cavities and tunnels in bulbs and roots. The larvae enter the soil to pupate, passing the summer in dormancy. In eastern Mediterranean countries, where onion and garlic are planted in autumn, the adults emerge at that time and remain active till spring. In northern countries, where such crops are grown mainly in summer, the onion maggot spends the winter in diapause, emerging in the spring. The threshold of development was calculated in the USA to be about 4.5 C°, and a generation requires 740 day degrees.
Economic importance: The most serious damage is caused by the pest’s first generation, which extends over several weeks due to female longevity. A single larva can attack several seedlings in succession, after which they wilt and die. Later in the season the leaves turn yellow and their bulbs rot, and larger plants may die, especially in damp weather. In addition the pest promotes the onset of fungal and bacterial rot. Some of the damage becomes evident only during the harvest.
Horticultural methods: Crop rotation can provide effective control. Other methods include removal of all infested plants, autumn digging of the ground to destroy the pupae, and early or late planting in different parts of the world. Early planting results in pest avoidance, whereas late planting reduces the time available for the overwintered flies to oviposit on the plants.
Monitoring: Yellow sticky cards and pheromone traps are in use.
Non-chemical methods: Barriers of nonwoven fibers of ethylene vinyl acetate significantly reduced the number of onion maggots infesting plants, a mode of control that achieved results comparable to those with insecticide applications.
Chemical control Drenching the soil with spinosad or organophosphate insecticides provides effective control. Some resistance to the pesticides has been reported. Another option is seed treatment with the pyrethroid Tefluthrin. An IGR was also effective, without affecting the co-applied Entomopathogenic nematodes .
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Davidson, G. and Chandler, D. 2005. Laboratory evaluation of entomopathogenic fungi against larvae and adults of onion maggot (Diptera: Anthomyiidae). Journal of Economic Entomology 98: 1848-1855.
Ellis, S. A. and Scatcherd, J.E. 2007. Bean seed fly (Delia platura, Delia florilega) and onion fly (Delia antiqua) incidence in England and an evaluation of chemical and biological control options. Annals of Applied Biology 151: 259-267.
Hoffmann, M.P., Kuhar, T.P., Baird, J.M., Gardner, J., Schwartz, P. and Shelton, A.M. 2001. Nonwoven fiber barriers for control of cabbage maggot and onion maggot (Diptera : Anthomyiidae). Journal of Economic Entomology 94: 1485-1491.
Liu, H.J., McEwen, F.L. and Ritcey, G. 1982. Forecasting events in the life cycle of the onion maggot, Hylemya antiqua (Diptera: Anthomyiidae): Application to control schemes. Environmental Entomology 11: 751-755.
Nault, B.A., Werling, B.P, Straub, R.W. and Nyrop, J.P. 2011. Delaying onion planting to control onion maggot (Diptera: Anthomyiidae): Efficacy and underlying mechanisms. Journal of Economic Entomology 104: 1622-1632.
Nault, B. A., Straub, R. W. and Taylor, A.G. 2006. Performance of novel insecticide seed treatments for managing onion maggot (Diptera: Anthomyiidae) in onion fields. Crop Protection 25: 58–65.
Yathom, S. 1960. Life History of the Onion Fly Hylemyia antiqua Meigen in Israel. Ph.D. thesis, Hebrew University of Jerusalem.
Yildirim, E. and Hoy, C.W. 2003 Interaction between cyromazine and the entomopathogenic nematode Heterorhabditis bacteriophora Poinar “GPS11” for control of onion maggot, Delia antiqua (Meigen). Crop Protection 22: 923-927.