HortFACT
Identification
Adult greasy cutworm, Agrotis ipsilon, is mottled brown to greyish brown with large areas of black on the forewings and thorax. The forewings are long and narrow and have a span of approximately 45 mm. The male antennae are feathery, and the female antennae are cord-like. They are nocturnal in habit, fly strongly, and are attracted to light. During the day they hide themselves among vegetation, but will fly away if disturbed.
Eggs are laid in random clusters or singly, on vegetation or on open ground. They are about 0.5 mm in diameter, and a female will produce between 20 and 2000 eggs depending on her size and the conditions. In general between 600 and 800 are laid. The eggs are whitish but turn light brown within 24 hours of being laid .
Young larvae [caterpillars] are brown to greyish, and larger larvae are dark grey with two yellowish longitudinal stripes above, and light grey below. There are five instars [larval stages], and fully-grown final-instar larvae may be up to 50 mm long and weigh up to 1.5 g. When well fed the larger larvae are plump, and the skin has a shiny, greasy appearance.
The young larvae forage on leafy growth until they are about one-third grown. At about this time their colour darkens to the typical greasy grey. They then descend to the ground, where they tunnel into the soil, emerging at night to feed, frequently dragging vegetation into their tunnels. When fully grown the larva starts the pre-pupal stage. It stops feeding and makes an earthen cell in the top 50 mm of soil, preferably under some moisture - conserving object like a piece of wood or a cow-pat.
Pupae are reddish brown but darken as emergence approaches. When the moth emerges it forces its way to the surface of the soil before it expands its wings and flies.
Host Plants
There is a wide range of host plants. Tomatoes, beans, brassicas, corn, and many other crops are damaged. Pastures often support many Agrotis, although the damage is not very noticeable; such numbers must cause considerable loss. Lucerne and clover are favoured by larvae as are the weeds dock (Rumex spp.) and plantain (Plantago spp.). Where infested land is adjacent to or converted to horticulture, the spread or carryover of Agrotis often causes substantial loss.
Damage
The young larvae feed on foliage, and as they are small at this stage, the damage is not generally very noticeable. Larger larvae also eat foliage, but they do a great deal more damage. The larger larvae also have a habit of cutting off plants and seedlings at ground level, thus destroying far more than they actually consume. It is the cutting-off habit, together with its appearance, which has earned for this species the common name of the greasy cutworm.
Distribution
Agrotis ipsilon is found in open areas below the winter snowline throughout New Zealand. It is present on Stewart Island, and has been found breeding on some of the more southern islands. The New Zealand species is also found in Australia, New Guinea, and other Pacific Islands.
There is strong evidence to suggest that New Zealand's population is frequently supplemented by migrants from Australia.
Another closely related species is found throughout most of the rest of the world.
Life-Cycle
| Egg |  |
| Larvae | |
| Pupae | |
| Adult | |
| Month | |
| Note: Coloured bars indicate periods of peak activity in each of the life cycle stages | |
Eggs hatch in 3-7 days, and the larval stage is usually about 4-6 weeks. The pupal stage lasts about 2-3 weeks, and there is a preoviposition period of 3-4 days before the female is able to lay fertile eggs. The normal summer life-cycle lasts between 7 and 10+ weeks, depending on the weather and locality. Up to three generations a year may occur in the warmer parts of New Zealand, and usually two generations in the cooler parts. Both larvae and pupae overwinter and may take up to 6 months to develop.
D. J. ALLAN