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Biology and behaviour of the Spur-throated locust
Number of generations
Oviposition and egg development
Nymphs
Adults
Migration
Economic impact
Number of generations
The spur-throated locust has one generation per year. Adult locusts live 10-12 months, from autumn of one year until the following summer.
Oviposition and egg development
The spur-throated locust spends the autumn and winter as immature adults in diapause. Egg maturation begins with the first rains in the wet season, usually during October/November and lasts 2-3 months. During dry years, spur-throated locusts in the arid zone may not lay until February or even March and in very dry years there may be no laying at all.
Like the Australian plague locust, the spur-throated locust lays its eggs in the soil. The female drills a hole into the ground using her ovipositor and lays the eggs in a group called a pod. A single pod may contain up to 160 eggs and each female has the potential to lay five pods within their life-span.
Unlike the Australian plague locust, female spur-throated locusts do not congregate when laying eggs and form 'egg beds'. Rather, egg laying occurs over a wider area although females tend to lay near areas of short grass, on headlands between crops or on banks of irrigation channels.
Eggs laid in moist soil take 20-30 days to develop depending on temperature. Eggs laid in dry soil enter a quiescent (resting) phase and do not hatch until further rain falls. However, unlike the Australian plague locust, spur-throated locust eggs are not able to stay in quiescence for prolonged periods and many die if the dry period continues for more than a month.
Nymphs
Nymphs of spur-throated locusts, unlike those of the Australian plague locust and migratory locust, do not aggregate into dense bands although they can be found in groups particularly where their favoured grasses are very restricted. Young nymphs are most common in short grasses and ephemerals while older nymphs are found in taller vegetation. When populations are high, such restricted areas can have quite high densities of nymphs though compact marching bands rarely form.
Nymphs take about 10 weeks to reach the adult (winged) stage and undergo 6-8 moults. Because nymphal development is so long, spur-throated locusts require at least two falls of summer rain, each of more than 40 mm, to ensure survival to the adult stage. When this doesn't occur, mortality is high and few survive to become adults.
Nymphs are usually present from December-March though if the wet season is delayed and hatching is late, nymphs can be present well into autumn.
Adults
Fledging usually occurs during March-April but can occur as early as February depending on when the eggs were laid. At the end of the wet season the newly fledged adults move to their winter habitat and roost in trees. When numbers are high they can defoliate trees and even cause branches to break.
As with eggs and nymphs, the development of adults to sexual maturity is slow when compared to other species of locusts. The growth stage takes at least 15 days for males and 20 days for females. Fat accumulation begins late in the growth stage but females are in diapause during autumn and winter. They do not mature eggs and lay until the next summer wet season, 7-9 months later.
Migration
The rains of the early wet season are often localised and to increase the chance of finding rain areas, spur-throated locusts undertake long distance migration. Short distance movement of spur-throated locust swarms may occur during the day but long distance migration only occurs at night, usually associated with the passage of low pressure systems or fronts. Between October and January massive adult population movements may occur when weather systems can carry the locusts from western areas of Queensland into cropping areas. Migrations of 700-1000 km have been recorded.
Economic impact
The spur-throated locust is a spasmodic but nevertheless important pest of agriculture in New South Wales, Queensland and Western Australia.
Spur-throated locusts feed on all types of crops unlike the Australian plague locust and migratory locust which are mainly restricted to gramineous crops. Summer crops (such as sorghum, sunflowers and soybeans) are particularly susceptible as they are present when the locusts are most active.
Damage to winter crops tends to occur in the autumn just after sowing when the locusts are fledging and at the late ripening stage in spring when the locusts are beginning to mature. However, extensive damage to wheat during the winter has been known to occur in crops adjacent to roosting sites.