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Brown shield bug

Brown shield bug (BSB) is one of several species known as podsucking bugs. It reduces crop yield and quality by feeding on developing seeds with its piercing-sucking mouthparts.

Scientific name

Dictyotus caenosus

Other names

  • Also known as the brown stink bug and, occasionally, the brown ground bug.

Description

  • Adults are 8mm long, shield-shaped and matte brown.
  • Eggs are pale cream, similar in shape to green vegetable bug (GVB) eggs, and laid in irregular or twin row rafts of 10–16 eggs.
  • Newly hatched nymphs are orange with black markings.
  • Larger nymphs have dark-brown to black heads and thoraxes, and a pale-brown abdomen with a pale band at the front and transverse dark-brown and pale markings in the centre.

May be confused with

Adults may be confused with the predatory glossy shield bug, which is glossy and slightly larger.

Distribution and habitat

A widespread but usually minor pest, BSB is occasionally reported in high numbers in summer pulses in western Darling Downs and northwest New South Wales.

BSB typically invades summer legumes at flowering, but are primarily pod feeders with a preference for pods with well-developed seeds. Summer legumes remain at risk until pods are hard (i.e. very close to harvest). Damaging populations are typically highest in late summer crops during late podfill (when nymphs have reached or are near adulthood).

Hosts

Soybean, mungbean, navy bean, azuki bean and cotton.

Damage

Similar to that caused by GVB (potential yield loss, and reduced seed quality), but BSB adults damage only ¾ as many seeds as GVB adults.

Life cycle

  • Nymphs grow through 5 stages and usually reach a damaging size during mid to late podfill.
  • Usually only one BSB generation develops per summer legume crop unless temperatures are high.

Monitoring and thresholds

  • Beat sheeting is the preferred sampling method.
  • Sample early to mid-morning when bugs are more likely to be at the top of the crop.
  • Look for the distinctive egg rafts, which indicate the presence of BSB.

Podsucking bugs other than GVB are converted to GVB equivalents, and decisions are made based on the GVB thresholds. An online calculator for mungbean and edible soybean is available at the Beatsheet.

Natural enemies

Spiders, ants, and predatory bugs are major predators of BSB eggs and young nymphs, with mortality sometimes exceeding 90%.

Eggs may be parasitised by the tiny wasp Trissolcus basalis.

Control

  • No insecticides are specifically registered against BSB in Australia. However, BSB may be incidentally controlled by pesticides targeting green vegetable bug.
  • Spring plantings are at lesser risk than summer planted crops.
  • Avoid sequential plantings of summer legumes, as this allows successive generations of podsucking bugs to build up.

Further information