Mythimna convecta

Mythimna convecta (Walker, 1857)
Australian Armyworm
(one synonym : Pseudaletia evansi Holloway, 1977)
HADENINAE, NOCTUIDAE, NOCTUOIDEA

Don Herbison-Evans
(donherbisonevans@yahoo.com)
and
Stella Crossley

Mythimna convecta
(Photo: courtesy of the Macleay Collection, Chau Chak Wing Museum, University of Sydney)

This Caterpillar is brown, with a narrow dark-edged pale stripe along the back, and two dark-edged pale stripes along each side of the back. The pale stripes continue over the thorax. The head is stippled in black and brown, with a dark-edged pale triangular frons and a dark-edged pale dorsal stripe.

close-up of head and thorax
(Photo: courtesy of David Akers, Won Wron, Victoria)

It is an agricultural pest, causing damage to pastures and crops. It hides by day, and feeds nocturnally on many plants, including :

Pineapple ( Ananas comosus, BROMELIACEAE ),

Sweet Potato ( Ipomoea batatas, CONVOLVULACEAE ),

Alfalfa ( Medicago sativa, FABACEAE ), and

various Grasses and Cereals ( POACEAE ).

They are called 'Army Worms' because of their habit of spreading out in a line across a lawn or pasture, and marching across it (somewhat slowly) consuming the foliage as they go.

(Photo: courtesy of the Macleay Collection, Chau Chak Wing Museum, University of Sydney)

The pupa is brown, and formed in a light cocoon in a cavity excavated just under the soil surface.

The adult moth has slender speckled rusty brown forewings with variable vague markings, each forewing usually with a black-edged white dot near the middle, next to a reddish smudge. Sometimes it has an angled submarginal line of dark dots. The hindwings are buff with dark veins and a broad dark margin. The hindwings have sinuous margins. The moth has a wingspan of about 4 cms.

(Photo: courtesy of the Photography Group, Centre for Biodiversity Genomics, University of Guelph)

The species is migratory, and has been found across most of Australia, including

Queensland,

Norfolk Island,

New South Wales,

Australian Capital Territory,

Victoria,

Tasmania,

South Australia, and

Western Australia.

underside
(Photo: courtesy of Joan Fearn, Moruya, New South Wales)

Sightings in Australia identified as Mythimna separata are often actually Mythimna convecta. The adult moths are superficially only distinguishable by the undersides of the hindwings. Mythimna convecta has a broad black marginal band visible under each hindwing, whereas Mythimna separata has plain brown hindwing undersides.

Attempts to control the pest include :

using a garden roller at midnight (when they are attacking a lawn),

digging post holes for the larvae to congregate in during the daytime, where they may be crushed,

laying some sacking near the plants attacked, so that the Caterpillars will hide under that by daytime, and they may be then collected and disposed of,

various chemical insecticides
(chlorpyrifos, alpha-cypermethrin, trichlorfon, carbaryl, methomyl)

a nuclear polyhedrosis virus,

the fungus Nomuraea rileyi,

the nematode Steinernema carpocapsae ( STEINERNEMATIDAE ),

a wasp Netelia species, ( ICHNEUMONIDAE ),

the wasp Apanteles ruficrus ( BRACONIDAE ), and

various flies, including Ceromya horma ( TACHINIDAE ).