HortFACT
Identification
Cosmopolitan Armyworm derives its name from the very large, epidemic populations which sometimes develop when the caterpillars move "as an army" through grass and cereal crops.
The adults have a wingspan of up to 40-50 mm and vary in colour from fairly uniform dull yellowish-brown to bright reddish brown. The forewings have a small central whitish spot. The hind wings are uniformly grey. Adults, which are nocturnal in habit, are strongly attracted to lights.
The eggs are pale cream, and are laid in clusters on the lower leaves of grasses, usually between blades or in sheaths, the mass being held in place by a sticky secretion.
Larvae [caterpillars] when fully grown are up to 40 mm long. The younger larvae are green, whereas larger larvae are pale greenish-brown with a thin whitish line down the back and dark lines on each side. There are also dark longitudinal lines near each side of the body. The head has a honeycomb pattern on it. Larvae pass through five instars [stages].
Pupae are reddish brown, and are found underground or beneath stones, etc.
Host Plants
Cosmopolitan Armyworms are essentially grass feeders and important as pests of pasture grasses, cereals, and maize.
Damage
Some losses of production of "grass" crops result from feeding by cosmopolitan Armyworm every season, but when populations reach epidemic proportions plants are completely stripped of foliage. Feeding is mostly on leaves but can also be on stalks, and in maize on developing cobs. In recent years populations appear to have been stabilised by parasitic hymenoptera (wasps). The remains of parasitised caterpillars complete with clusters of 10-20 yellow to greyish coccoons can often be seen adhering to plant material or fence posts.
Distribution
Cosmopolitan Armyworm is recorded in south-east Asia, eastern Australia, and some Pacific Islands. In New Zealand it is distributed throughout the North Island and in the Marlborough and Nelson Provinces in the South Island. Distribution in New Zealand is probably affected by climate, as the species is more common in the North Island.
Life Cycle
| Egg |  |
| Larvae | |
| Pupae | |
| Adult | |
| Month | |
| Note: Coloured bars indicate periods of peak activity in each of the life cycle stages | |
The spring flight of moths results from overwintering larvae. Larval development takes approximately 1 month, the duration varying according to the weather. The development times are greatly extended during the colder winter months. There are at least three generations in a year.
E. W. VALENTINE - Revised by DJ Allan.