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Biology and behaviour of the Migratory locust
Oviposition and egg development
Nymphs
Adults
Migration
Economic impact
Oviposition and egg development
While the migratory locust often matures and lays after rain, it will mature and lay after 2-3 weeks even when the vegetation is drying off. Unlike the Australian plague locust, eggs of the migratory locust survive for only a short period in dry conditions. Also, in central Queensland, the area most commonly infested with migratory locusts, winter temperatures are usually too high for eggs to enter a diapause stage. Consequently, if the soil becomes dry after laying survival of the eggs is poor and substantial mortality occurs unless rain falls at regular intervals throughout the year.
Like the Australian plague locust, the migratory locust lays its eggs in defined areas known as egg beds. Favoured sites include: moist soil in areas of cultivation , silt beds resulting from erosion, semi-dry creek beds or even ratoon sorghum crops in silted areas.
Each egg pod may contain 50 to 60 eggs and a single female may lay 3 to 5 egg pods during her lifetime. The eggs take about 11-15 days to develop depending on temperature.
Nymphs
At normal temperatures nymphs develop in about 30 days and undergo 5-6 moults before the adult stage is reached. However, in dry and cold weather development can take considerably longer.
When nymphs are present in large numbers they become highly gregarious and aggregate into dense, compact bands (up to 1500/m2 covering an area of 5 ha) with a characteristic marching movement. These bands can move considerable distances, up to 500 m/day, depending on vegetation conditions.
Adults
Under normal summer temperatures, adult migratory locusts live for about two months. They become sexually mature in about 14 days following fledging and usually form into dense swarms.
The females are capable of laying an egg pod every 4 to 6 days. As this locust can develop rapidly, when conditions are favourable, five to six generations may be possible in a year. Often these generations overlap and all stages of locusts may be present within a given area.
Migration
The migratory locust can migrate long distances but tends to do so less often than the Australian plague locust However, sometimes swarms in the Central Highlands of Queensland move westwards and may reach Blackall, Barcaldine and Longreach, approximately 400 km away.
Economic impact
Due to the limited distribution of migratory locust in Australia, this species is perhaps the least important except in the Central Highlands of Queensland where it is frequently a pest.
Both the nymphs and adults of migratory locusts are voracious feeders and when present in high numbers they can cause considerable damage.
Below: Sorghum crop damaged by Migratory locusts nymphs
Migratory locusts are primarily grass feeders, attacking pastures and crops such as sugarcane, sorghum, wheat, barley, oats and maize. Unlike the spur-throated locust, it does not readily attack non-gramineous crops such as sunflowers and soybeans.