Cotesia ruficrus wasp.
Source: Crop and Food Research Biocontrol agent:
Armyworms and cutworms
What do Cotesia ruficrus wasps look like?
Cotesia ruficrus is a tiny, parasitic wasp about 2.0-2.5mm in length. The females have a short, pointed ovipositor through which eggs are injected ('stung') into host caterpillars.
What about their life cycle?
Each female lays about 250 eggs during a lifespan of approximately two weeks, injecting them inside the host caterpillars in batches of about thirty. Larvae hatch from the eggs and feed on the body fluids of the host. Fully grown larvae force their way through the host's body wall, emerging to spin a number of white, fluffy cocoons about 4mm in length and grouped in masses.
Host caterpillars die within 24 hours of parasite emergence. Pupae begin to develop in cocoons within about two days of cocoon formation, and five days later the adult cuts a circular hole in the cocoon and emerges. Mating occurs almost immediately after emergence, and females are then able to parasitise new hosts.
Where are they established?
Cotesia ruficrus are widespread throughout Northland
When and how are they best harvested for redistribution?
Collect the fluffy, white cocoons often seen adhering to plant material or fence posts. Transfer them to infested crops. Alternatively, collect late instar larvae and keep them in a two-litre ice cream container with the host food, and cover with fine mesh. Collect the cocoons for redistribution.
What do the host armyworm look like, and how do they damage plants?
Armyworm is the term for the larvae (caterpillars) of a number of species of moth that, when high in number, appear to march through a crop. The larvae are variable in colour - green at smaller, younger stages, through to green, brown or grey for older, larger larvae (up to 50mm long). The fully grown larvae burrow a short distance into the soil to pupate, emerging from January to May as reddish brown pupae.
Cosmopolitan armyworms (Mythimna separata) are grass feeders and important as pests of pasture grasses, cereals and maize. They vary in colour from fairly uniform dull yellowish-brown to bright reddish brown. The forewings have a small central whitish spot with the hind wings being uniformly grey. The moths are nocturnal, and are strongly attracted to light.
What do the host greasy cutworm look like, and how do they damage plants?
The young larvae (caterpillars) are brown to greyish, with larger larvae being 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 50mm long. The larger larvae are plump, and the skin has a shiny, greasy appearance. Larvae are found through spring and summer and feed on tomatoes, beans, brassicas and corn. They pupate in the soil and are reddish brown.
The moth is mottled brown to greyish brown with large areas of black on the forewings and thorax. The forewings are long and narrow, with 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.
The larger larvae also have a habit of cutting off plants and seedlings at ground level, thus destroying the plant. It is this cutting-off habit, together with its greasy appearance, that gives this species its common name of greasy cutworm.