Green vegetable bug

Green vegetable bugs (GVB) attack all summer and winter pulses (except chickpea) and are a major pest of soybeans, especially in coastal areas. GVB is the most damaging podsucking bug in pulses, because of its abundance, widespread distribution, rate of damage, and rate of reproduction.

Scientific name

Nezara viridula

Description

Adults are bright green, shield-shaped, 13–15mm long with 3 small, white spots between their shoulders.

  • Occasionally yellow or orange.
  • Can darken to purple-brown when overwintering.
  • Emit a foul smell when disturbed to deter predators.

Eggs are laid in rafts (50–100 eggs per raft).

  • Eggs are circular in cross section.
  • Newly-laid eggs are cream but turn bright orange prior to hatching.
  • Parasitised GVB eggs are black.

Nymphs change colour and shape as they develop.

  • Newly hatched nymphs (1.5mm long) are orange and brown, and sometimes black.
  • Younger nymphs are round or oval rather than shield-shaped.
  • Later instars are either green or black, with white, cream, orange and red markings.
  • Final (5th) instar nymphs have less patterning and prominent wing buds.

Younger nymphs usually aggregate in large clusters, while older nymphs disperse more widely.

May be confused with

Adult bugs may be confused with:

Parasitised GVB eggs may be confused with predatory shield bug eggs but lack the spines around the top of the eggs.

Distribution and habitat

Widespread in warmer areas.

Adult bugs typically invade summer legumes at flowering, but GVB is primarily a pod feeder and prefers well-developed seeds. Summer legumes remain at risk until pods become too hard to damage (i.e. very close to harvest).

Hosts

Soybean, mungbean, navy bean, azuki bean, peanut, cotton, sunflower, linseed, maize, and many horticultural crops.

Damage

GVB use their long, thin mouthpart to suck nutrients from the seed (stinging the seed).

  • Nymphs usually reach a damaging size mid to late podfill, as they require seeds to complete their development.
  • Damage to young pods produces deformed and shrivelled seeds, reducing yield.
  • Damage to seeds in older pods results in blemishing, and they are difficult to grade, reducing harvested seed quality.

GVB also damages buds and flowers, but soybeans compensate for this early damage.

Life cycle

  • Eggs take 6 days to hatch at 25°C.
  • Nymphs have 5 instars with a total development time of 30 days.
  • High mortality at temperatures above 35°C.
  • In Queensland, GVB has 3–4 generations during the summer.
  • GVB adults survive winter by sheltering in places such as mature maize crops, under tree bark, or in farm buildings.

The podding phase of most summer legumes is only slightly longer than GVB´s life cycle, so usually only 1 generation develops per crop, but populations can move progressively from earlier to later plantings, and eventually build to very high levels.

Monitoring and thresholds

Beat sheet sampling is the most efficient monitoring method:

  • Inspect crops twice weekly from budding until close to harvest.
  • Sample early to mid-morning when bugs bask at the top of the crop canopy.

Edible soybean thresholds are linked to seed quality, and are therefore very low. Crushing and stockfeed soybeans have a higher threshold.

An online calculator for mungbean and edible soybean is available at the Beatsheet.

Natural enemies

  • GVB eggs are frequently parasitised by the tiny wasp Trissolcus basalis. Parasitised eggs turn black.
  • GVB nymphs are attacked by ants, spiders and predatory bugs.
  • Final (5th) instar and adult GVB are parasitised by the tachinid fly, Trichopoda giacomellii.

Control

  • Control bugs during early podfill before nymphs reach a damaging size.
  • Avoid sequential plantings of summer legumes.
  • Avoid combining cultivar and planting times that could lengthen the duration of flowering and podding.

Further information

Contact

General enquiries 13 25 23