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Brown bean bug

Brown bean bugs can be an infrequent but major pest of many legume crops, and are as damaging as the green vegetable bug.

Scientific name

Riptortus serripes—large brown bean bug (LBBB)
Melanacanthus scutellaris—small brown bean bug (SBBB)

Other names

  • In the past, Riptortus serripes has been referred to as the 'brown bean bug' or the 'podsucking bug'. The preferred common name is now the 'large brown bean bug' to avoid confusion.

Description

Adults are brown and elongated, with long antennae and robust, spiny hind legs.

  • LBBB has a bright yellow stripe along each side (paler in females), and a prominent spine on each shoulder.
  • SBBB has a cream stripe along each side (males also have a pale patch on the upper back) and smaller shoulder spines.

Eggs are slightly elliptical with a flat top and laid singly or in small clusters.

  • LBBB are dark purple-brown and 1.5mm long
  • SBBB are shiny olive green and 1mm long.

Nymphs are dark brown and are similar in outline to ants. The abdomen of later instar SBBB is more elongated than LBBB.

May be confused with

Nymphs can be mistaken for ants, but lack the very narrow 'waist' and biting mouthparts (jaws).

Distribution and habitat

Native to Australia; they are widespread in warmer areas.

Hosts

All summer and winter pulses (except chickpeas).

  • LBBB prefers mungbean, cowpea and adzuki bean.
  • SBBB favours soybean.

A minor pest in cotton and many horticultural crops.

Damage

Damage symptoms are similar to those of the green vegetable bug (GVB). Early damage reduces yield, while later damage reduces the quality of harvested seed.

Life cycle

  • Adults typically invade summer legumes at flowering.
  • Under laboratory conditions, individual females can lay 5–6 eggs per day.
  • Nymphs usually reach a damaging size by mid to late podfill.
  • Development time from egg to adult (through 5 nymphal stages) is about 25–26 days.
  • Overwintering LBBB may shelter in curled-up, dead leaves.

Monitoring and thresholds

Beat sheet counts may underestimate numbers as adult bugs are very flighty—monitor crops early morning and watch for adults flying away.

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.

Control

Brown bean bugs may be incidentally controlled by products used against the green vegetable bug. There are no products registered specifically for brown bean bugs in pulse crops.

Further information