Mythimna separata (Walker, 1865)
Oriental Armyworm
 (one synonym : Leucania consimilis)
HADENINAE,   NOCTUIDAE,   NOCTUOIDEA
 
Don Herbison-Evans
(donherbisonevans@yahoo.com)
and
Stella Crossley

Mythimna separata
Photo: courtesy of H.C. Sharma,
International Crops Research Institute for the Semi-Arid Tropics,
ICRISAT, Andhra Pradesh, India

The young Caterpillars are green. Later instars are brownish with a thin pale dorsal line, and with dark lateral lines on each side. The head has a light and dark brown pattern. Solitary individuals remain fairly pale in colour, but when caterpillars become crowded, for example when feeding communally, they develop a much darker shade.

The caterpillar is an international pest, attacking many agricultural plant species, particularly those in POACEAE such as

  • Maize ( Zea mays ),
  • Sorghum ( Sorghum bicolor ), and
  • Rice ( Oryza sativa ).

    The caterpillars feed on the leaves typically leaving only the midrib uneaten.

    The caterpillar will not feed on plants in other familes, which have various poisonous substances like the triterpenoid glucoside: Momordicine II.

    When the leaves of the foodplant are damaged by the caterpillars, some plants defend themselves by the release a chemical that attracts parasitic wasps to the area. The caterpillars of Mythimna separata are able to detect this chemical, and they hide when concentrations become dangerous to them.

    The caterpillars grow to a length of about 4 cms. The pupa is brown, and formed under surface litter in the soil.

    Mythimna separata
    (Photo: courtesy of Graeme Cocks, Townsville, Queensland)

    The adult moth has brown forewings with dark specks. The hindwings are pale brown. The pheromones of this species have been identified.

    Mythimna separata
    (Photo: courtesy of CSIRO/BIO Photography Group, Centre for Biodiversity Genomics, University of Guelph)

    The eggs of this species are off-white. They are laid in groups low on the leaves of a foodplant, often between in the sheaths or on the blades. The mother moth uses a sticky secretion to hold the group in place.

    The adult moths are given to mass migrations that have been tracked by radar.

    The species is found in, and often a pest in:

  • China,
  • New Zealand,
  • Japan,
  • Punjab,

    as well as in Australia in

  • Western Australia,
  • Northern Territory,
  • Queensland,
  • New South Wales,
  • Norfolk Island,
  • Victoria, and
  • South Australia.

    Various methods are used to control the caterpillars, including :

  • the use of Carbaryl 85% WP at 45 g/20 l of water,
  • the fly Exorista japonica ( TACHINIDAE ),
  • the wasp Apanteles kariyai ( BRACONIDAE ), and
  • a Nuclear Polyhedrosis Virus,.

    Further reading :

    Ian F.B. Common,
    Moths of Australia,
    Melbourne University Press, 1990, pp. 33, 45-46, 59, 65, 466.

    K. Shiojiri, R. Ozawa, and J. Takabayashi,
    Plant volatiles, rather than light, determine the nocturnal behavior of a caterpillar,
    PLOS Biology 4(6): e164 (June 2006)

    Francis Walker,
    Catalogue of Lepidoptera Heterocera,
    List of the Specimens of Lepidopterous Insects in the Collection of the British Museum,
    Part 32, Supplement part 2 (1865), pp. 626-627.

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    (updated 1 December 2012, 20 April 2021)