Bean fly

  • Image of bean fly adult on plant material
    Adult bean fly showing shiny, black body with clear wings (Photo: J. Wessels)
  • Bean fly larva tunnel under the surface of the stem, infestations can cause plant death
    Bean fly larva tunnelling into the surface of stem (centre, top stem) (Photo: J. Wessels)

General information

A stem damaging fly that attacks many legume crops. Capable of causing premature plant death, especially in seedlings.

Scientific name

Ophiomyia phaseoli

Description

Adults are small (3 mm long) and shiny black with clear wings. The larvae (or maggots) are cream with dark mouthparts and reach 3 mm in length. Pupae are small, brown and cylindrical with rounded ends.

Similar species

Soybean podfly (a minor pest only attacking pods).

Distribution

In Australia, bean fly is most common in tropical and subtropical coastal and subcoastal regions. It is generally not a problem in inland cropping areas, but is a worldwide pest of legumes.

Crops attacked

Favourite crops are navy beans, adzuki beans and mungbeans. Rarely a problem in soybeans.

Life cycle

Female flies lay their eggs in young leaves. After hatching, the larvae tunnel their way to the leaf mid vein, make their way to the petiole and stem and pupate in the lower stem.

Damage

Larval tunnelling damages the plants vascular tissue, causing reduced plant vigour and petiole droop in older crops. Severe infestations can cause seedling death. Crops are at greatest risk for three to four weeks from emergence, but later crops are sometimes attacked.

Monitoring and action level

Monitor seedling crops twice weekly. Look for the distinctive pale oviposition pinprick windows in the leaves and for larval tunnelling at the base of petioles and in the stems. Look for pupae, damaged stem tissue in the lower stems, and for adult flies. Take action if more than one larval tunnel per plant.

Chemical control

Control is readily achieved in young crops with systemic pesticides, but repeat sprays (within 7 days) may be required for heavy infestations. Spraying against bean fly in mature crops may not be cost effective. For current chemical control options, see Pest Genie or APVMA.

Cultural control

Ensure cropping areas are free of weed hosts, such as phasey bean and volunteer crop legumes.

References

  • Crop insects: the ute guide Northern Grain Belt.
  • Pests of field crops and pastures: identification and control. Editor: P.T. Bailey.

Last updated 25 June 2010