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Blue butterflies

Although most lepidopteran pests of field crops are moths, 2 species of blue butterflies can be found in pulses. (The cabbage white butterfly may occur in canola.)

Scientific name

Lampides boeticus (pea blue butterfly)
Zizina otis labradus (common grass-blue butterfly)

Other names

  • Common grass-blue butterfly is also known as grass blue butterfly.
  • Pea blue butterfly is also known as long-tailed pea-blue butterfly or lucerne blue butterfly.

Description

Pea blue butterfly

  • Wingspan is about 26mm.
  • Wings are blue with wide, dark brown edges on top, and light brown with pale stripes (including a broad band across both wings) underneath.
  • Hindwings have a small, thin tail with 2 small, black eye spots at the base of each tail. The eye spots are ringed with orange on the underside.
  • Larvae are 10mm long and pale cream to pale pink. The pale brown head retracts when disturbed.

Common grass-blue butterfly

  • Adults are slightly smaller than pea blue butterflies.
  • Wings are pale, dull blue on top with dark grey edgings, and light brown with soft markings underneath.
  • Eggs (0.5mm) are flattened with a central depression and have a bluish tinge.
  • Larvae are 10mm long, pale green and slug-like with pale stripes and small hairs on their back. The head is usually tucked out of sight.

May be confused with

Common grass-blue larvae may be confused with hoverfly larvae. Look on the larva's underside—butterfly larvae have legs, hoverfly larvae don't.

Distribution and habitat

Both species are widespread in Australia but are usually only minor or infrequent pests.

Hosts

  • Pea blue butterfly occurs in a range of legume species. The risk period is during budding and flowering.
  • Common grass-blue butterfly feeds on many pulse crops and pasture legumes but is most commonly found on soybeans.

Damage

Pea blue butterfly larvae eat buds and flowers but may also damage small pods.

Common grass-blue butterfly larvae usually feed on leaves and terminals but can also attack flowers and pods. Windowing damage to leaves (see image above) is usually not economic to control, but significant damage to terminals can result in more pods developing close to the ground, making plants difficult to harvest.

Monitoring and thresholds

  • Look for the distinctive adult butterflies in crops.
  • Carefully examine inside buds and flowers for pea blue butterfly larvae and/or damage.
  • Use a beat sheet to check for common grass-blue butterfly larvae, and also look for larvae and damage in terminals. Control if terminal loss exceeds 25%.

Control

  • Most products targeting helicoverpa (except NPV) will incidentally control blue butterflies.
  • Irrigation of crops at flowering will improve plant vigour and allow the crop to replace damaged flowers and terminals.

Further information