Locust situation 02 September 2021
This page summarises the known distribution of locusts during autumn 2021 and provides a brief outlook to September 2021. Regional information and forecasts are given in the latest Locust Bulletin.
Australian Plague Locust (Chortoicetes terminifera)
The locust population in inland eastern Australia declined significantly during autumn. Adult numbers had reduced to low – medium levels over much of the interior by May from much higher densities identified earlier, which had included some long, narrow swarms observed in mid-February very closely associated with drainage lines in parts of the Channel Country of Queensland and several swarms detected in early March in Hillston and Hay districts of the Riverina of New South Wales. Apart from a small Sub-band density of nymphs identified in the north of Jerilderie of the Riverina of NSW in early March, only occasional low-density nymphs were observed by ground surveys, and no bands were detected in the Queensland Channel Country and surrounding areas by aerial surveys during late March and early April. Most eggs laid in autumn would have undergone overwintering in either diapause/quiescence or slow development, with only a small proportion hatching prior to the onset of winter. Widespread rainfall and flooding in March hampered ground survey of areas where large locust populations had previously been identified. Weather patterns, detections by the insect monitoring radar in Hay, light-trap captures in White Cliffs, Fowlers Gap and Dulkaninna, and public reports indicate several occurrences of short-distance migration, with likely redistributions of the adult population prior to egg-laying. No surveys were conducted in Victoria and no reports were received, but locust populations are expected to remain at low levels in that State.
Rainfall for autumn was slightly below average over inland eastern Australia, about average over much of Queensland, above to very much above average over much of the North East Pastoral of South Australia and the North West and Central West of NSW, but below to very much below average over south-western NSW, north-western Victoria and south-eastern SA districts. The total rainfall for autumn ranged from less than 25 mm in the southern part to more than 300 mm in the eastern part, mainly received in March, while the interior had nil or less than 25 mm in April and May (below to very much below average). Mean temperature for autumn over the eastern interior was generally below average. It was above average over much of the North West and Central West of Queensland but below to very much below average over central and northern NSW and adjacent southern Queensland, while about average over much of south-western NSW, Victoria and SA regions. This was mainly attributed to lower minimum temperature over inland NSW and adjacent areas. The La Niña event had ended in March and the El Niño–Southern Oscillation (ENSO) remained neutral during winter and likely persists in spring. Rainfall and temperatures are expected to return to normal seasonal patterns with slightly wetter spring. With about average rainfall and warmer temperature for winter, the overwintering locust populations are likely to have experienced faster development.
The spring outlook is for possible early nymphs hatching in late winter in sub-tropical Queensland, and possible localised high-density nymphs developing in late September in the Riverina of NSW and adjacent areas. It is expected that some bands may develop and result in localised high-density spring populations in the Riverina and adjacent areas, and some low – medium density nymphs in parts of Queensland.
There is a low likelihood of widespread high-density populations and region-wide infestations developing in spring, but possible localised high-density populations and limited infestations in parts of New South Wales.
Spur–throated Locust (Austracris guttulosa)
Surveys detected consistent occurrences of Present-density nymphs and Isolated – Numerous-density adults in the Clermont-Roma and Longreach-Winton areas of Queensland. Only occasional adults were identified in New South Wales and South Australia. Isolated high-density adults were reported in localised areas of the Queensland Gulf region in late winter.
With sufficient rainfall and warmer temperatures in tropical and sub-tropical Queensland, it is possible for localised low – medium-density adult populations to persist though winter.
There is a low risk of a widespread infestation, but localised higher density infestations may develop in subtropical Queensland during the winter and spring.
Migratory Locust (Locusta migratoria)
Surveys in mid-March detected occasional Isolated – Scattered-density adults in the Clermont-Injune areas of Queensland. Improved habitat conditions in the Central Highlands and Coalfields and the Darling Downs and Granite Belt regions of Queensland may have encouraged some localised breeding. High-density gregarisation is unlikely to result from the current very low background level.
There is a very low risk of a widespread infestation developing during the winter and spring.