Delia coarctata

Scientific Name Delia coarctata (Fallén)
Common Names English: Wheat bulb fly; German: Brachfliege; French: Mouche grise des céréales; Spanish: Mosca gris de los cereales
Description The adult looks similar to a house-fly but is only 6-7 mm (0.24-0.27 inch) in length, with a body of yellowish-brown or gray color. The maggots are white and up to 10-12 mm (0.39-0.47 inch) in length.

Biology

Damage

Depending on soil temperatures, larvae of D. coarctata hatch between the end of January and mid-March. They move through the soil to find the host plant, and then bore into its base, after which they start feeding on the central shoot, causing it to wilt and die off („deadheart symptoms“): the outer leaves will remain undamaged. Each larva can attack several (6-7) shoots in succession. If necessary, the maggots will later move through the soil to find another plant. Feeding ends in May, when pupation takes place.
If the host plants have not yet started tillering at the time of the attack, the crop may be completely destroyed.

Lifecycle

D. coarctata only has one generation per year. The adult flies emerge from their pupae in the soil from June onwards. After mating, the female lays about 40 single eggs during the period July-September, preferably on bare ground. The most attractive oviposition sites are characterized by loose, crumbly soil, e.g. in freshly cultivated areas, but also in fallow or set-aside, or in fields cultivated with cereals, peas, rape, potato, corn or other crops that leave areas of bare ground during the summer months. Hatching can only occur after the eggs have been exposed to temperatures below 12°C (53.6°F) for at least 4-6 months. On average, 40% of the eggs will result in active larvae: after cold winters, large numbers of larvae may emerge almost synchronously as soon as temperatures rise.
D. coarctata does not migrate over long distances, so the severity of attack will vary strongly between locations. It is a pest throughout Europe and the cereal-growing countries of the former USSR, in parts of North Africa and the Middle East, and in North America.

Occurrence

Additional Crop Information

Also barley, rye and various grasses.

Agricultural Importance

The extent of damage varies greatly. In most cases, the pest can be kept in check by cultural methods. Sometimes, however, infestation will be so severe as to require ploughing-in the crop, especially if plants only have single shoots at the time of hatching.

Control

Integrated Crop Management

Avoid creating favorable egg-laying conditions during the summer in fields that are due to be sown with cereals. Sowing early in autumn will reduce damage. Fallow areas not planned for cereals can divert egg-laying and lessen the impact on other fields. Couch grass attracts D. coarctata, being its natural host, and should therefore be carefully removed.

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