Tomato fruitworm wasps
Cotesia kuzak (top), with single cocoon, and Microplitis croceipes (bottom), with single cocoon.
Source: Crop and Food Research Biocontrol agents:
Two parasitic wasps - Cotesia kuzak and Microplitis croceipes
What do the wasps look like?
These small, black wasps, measuring 3-5 mm in length, have been very successful as biocontrol agents. Parasitism has resulted in a 95 percent reduction in insecticide use for tomato fruitworm.
What about their life cycle?
The wasp lays eggs in the early instar larva which hatch inside the larva, feed on it and eventually kill it. The wasp larva emerges to pupate and spins a single white cocoon from which an adult wasp will emerge to continue the cycle.
Where are they established?
Cotesia kuzak is widespread throughout Northland, while the distribution of Microplitis croceipes in Northland is unknown at present.
When and how are they best harvested for redistribution?
Collect tomato fruitworm larvae from damaged fruit or maize/corn cobs and place in a two-litre icecream container with the host food. Cover the container with a fine mesh cloth. Collect the parasitoid cocoons as they are spun next to the dead larvae and release on or near the crop to be protected.
How does the tomato fruitworm damage plants?
The larvae (caterpillars) are the damaging stage of this pest, feeding on a wide range of plants. Larvae feed mainly on flower buds, flowers, developing seed and fruits, and sometimes on foliage. They are a major pest on maize, tomato, lucerne, lupins, and pine seedlings, but also feed on peas and beans, pumpkins and marrows, tobacco and clover. They are found throughout Northland, and on tomatoes and beans the larvae bore completely into the fruit. On maize, after eating the silks, they feed on the soft seeds at the top of the cob. Foliage can be completely stripped from pine seedlings.
What does the tomato fruitworm look like?
The colour of the larvae can vary even on a single food host, ranging from shades of green to pink, brown or almost black. There is a double dark line down the middle of the back, and a broad pale stripe runs along each side of the body. There are five instars (larval stages), and fully-grown larvae are about 35-40 mm long.
Moths also vary in colour, but are typically brown to greyish brown with a series of dark, irregular, transverse lines across the front wing. There is a darker area towards the tip with a paler band near the margin and dark spot almost at the centre. Hind wings are pale at the bases with the outer half of each much darker. Adult moths have a wingspan of about 35 mm, are nocturnal in habit, flying, mating and laying eggs at dusk.
Pupation occurs in smooth-walled cells underground. The pupae overwinter in the soil, and, in Northland, the adults emerge with the warmer spring weather in early October.