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Cluster caterpillar

Cluster caterpillar is named for the high density ‘clustering’ of its young larvae, which initially feed close to the hatched egg mass. Cluster caterpillars are related to some of the armyworm species.

Scientific name

Spodoptera litura

Other names

  • Tobacco cutworm
  • Cotton leafworm

Description

Eggs

  • Pinkish to orange
  • Laid in clusters covered in brownish scales

Larvae

  • Smooth skinned (no hairs) and up to 40mm long
  • Pale or translucent green when young
  • Medium larvae develop noticeable dark spots slightly back from the head (see photo above)
  • Older larvae develop 3 lengthwise, thin orange stripes, 2 bands of dark half-moon shapes along their back, and a row of dark spots along the sides on the body

Pupae

  • About 20mm long
  • Reddish brown
  • Found in soil below the host plant

Adults

  • Moths are nocturnal
  • 20mm long with a 30–40mm wingspan
  • Forewings have a grey and reddish brown pattern
  • Hindwings are translucent white with a brown margin

May be confused with

Small to medium larvae (10mm long) may be confused with helicoverpa larvae but are distinguished by the darkened areas behind the head (medium larvae), and the rows of large dark spots.

Lawn armyworm (Spodoptera mauritia) also has rows of crescent shapes along the back but lacks the rows of dark spots along the sides.

Distribution and habitat

  • Occurs from India to the Pacific.
  • More common in tropical and coastal regions.

Hosts

Wide host range including cotton, legumes and brassicas. They also occur in many other horticultural crops and broadleaf weeds.

Damage

Young larvae feed on the leaf surface; older larvae may also feed on flowers and pods. In peanuts, older larvae can attack and sever pegs causing pod death.

Life cycle

  • Eggs hatch in 2–3 days.
  • Development though 6 instar stages and pupa to adult takes about a month.

Monitoring and thresholds

  • Look for the distinctive egg masses and clusters of young larvae.
  • In vegetative pulse crops, the defoliation threshold is 33%; in flowering/podding crops this drops to 15–20%.

Natural enemies

Natural control by a range of predators, parasitoids and pathogens usually keeps populations at low levels.

Current commercially available nucleopolyhedroviruses (NPVs) are specific to helicoverpa and will not work on Spodoptera species.

Control

Cluster caterpillars are incidentally controlled by most conventional pesticides targeting helicoverpa. Biopesticide options are limited as NPV formulations for helicoverpa will have no impact, and larger larvae are difficult to control with Bt (Bacillus thuringiensis).

Thorough coverage is required in peanuts to reach cluster caterpillars attacking pegs and exposed pods at the base of the plants.

For current chemical control options, search for registered chemicals.

Further information