HortFACT
Identification
The adult cricket is about 2.5 cm long; the body and wings are chestnut-brown. The head is large and black and bears a pair of very long antennae. The wings when folded back form a point which extends beyond the body, and on each side of this point a pair of hairy cerci are angled outwards and upwards to form a distinctive 'V'. The females in addition have a long, spear-shaped ovipositor [egg-laying tube] which protrudes below the overhanging wing tips. Only the adult males chirp, which they do by rubbing their wings together.
The eggs are white, sausage-shaped, and about 0.3 cm long. They are laid singly, but loosely clustered, about 1 cm deep in damp soil.
The nymphs [immature forms] are like small adults, but their wings and ovipositors are undeveloped. There are 9 or 10 nymphal instars [stages], the 1st instar being about the size of the egg. On the 8th and 9th (pre-adult) instars the developing wing buds plus the developing ovipositor on the females can be seen. A distinctive white band around their middle distinguishes the nymphs of this cricket from those of any other found in New Zealand.
Host plants
Adults and all nymphal ,instars feed most commonly on the leaves and germinating seeds of pasture plants, especially ryegrasses.
Damage
The damage done to pastures can be divided into three types:
(1) Grazing: adults and the larger nymphs compete with stock for available food. Over an area of 4000 sq.m (about an acre), a population of 20,000 crickets (i.e. 5 per sq. m) daily consumes as much as one sheep. In plague seasons as many as 20-40 crickets per sq. m frequently occur.
(2) During long drought periods the growing crowns of grasses are attacked; this often kills the plants and leaves the soil open to weed invasion.
(3) Seedling attack: later in the season seedlings, whether self-sown or in reseeded pasture, may be destroyed.
Distribution
Although the black field cricket is found throughout the grassland areas of the North Island and in the milder, coastal regions of the South Island, sufficient numbers to be of economic significance occur only in Northland, Auckland, and parts of Hawke's Bay and Taranaki.
Life Cycle
| Egg |  |
| Immature Nymphs |
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| Nymphs | |
| Adult | |
| Month | |
| Note: Coloured bars indicate periods of peak activity in each of the life cycle stages | |
The black field cricket has only one generation a year, but the life stages overlap considerably.
Overwintering takes place in the egg stage; eggs enter diapause [a resting state] a few days after being laid and then require a prolonged cold period before they will hatch. From hatching the nymphs take 2-4 months to grow into adults, which then live for 2-3 months. The females lay throughout almost their entire life-span, producing some 500-2000 eggs.
The smaller nymphs live and hide within the pasture, and this makes them very difficult to detect. Adults and the larger nymphs, when not feeding, tend to shelter in cracks in the soil or under dried-out cow-pats or any other suitable litter. Although this cricket is essentially a ground living animal, in plague years there are occasional mass flights from particularly densely populated areas.
A G SMITH