PEST
 
   NAME
     Fly Maggots
     Delia species
 
   ORDER
     Diptera
 
   FAMILY
     Aleyrodidae

Description of the Pest
The adult Onion Fly Maggot (Delia antiqua)  is a small grey-brown hairy fly to 5mm long and lays its eggs on decaying plant material. The ensuing whitish maggots are up to 8mm long, tapering towards the head and feed under ground.

   Onion Fly Maggot

Life Cycle
This insect has a Holometabolous life cycle, ie. When metamorphosis is observed during the pupal stage.
It has up to two generations per year.

Period of Activity and Distribution of the Pest
This pest is found from tropical to temperate regions and is most active during warm weather. Adult flies are commonly seen hovering over garden beds that have had manure added.

Susceptible Plants
This pest attacks Allium species particularly onions. Beans, crucifers and cucurbits are also attacked.

Cynodon dactylon (Couch) turf grass is susceptible to the CouchTip Maggot (Delia urbana). The eggs are deposited by the small fly and the larvae are tiny white maggots that eat the growing points of the grass. It is only a serious problem when there are large numbers of maggots.

Damage Caused
The larvae tunnels into the stem of the host then moves to the below ground parts. Bulbs and roots are hollowed out causing the plant to turn yellow, wilt and collapse. Infected plants generally lack vigour. These holes allow a secondary infection to enter the plant.

Cultural Control
Correct soil preparation reduces infestation. Avoid planting in soil that has uncomposted organic material in it, particularly when it is dug into the bed. Mulching should be carried out during mid summer or in mid winter when the adults are less active. 
This pest is difficult to eradicate and in an enclosed environment sticky fly paper can reduce numbers.

Biological control 
There is no effective biological control.

Chemical control
The soil may be treated with primiphosmethyl to aid in control. 
Note
Always read the label for registration details and direction of use prior to application of any chemicals.