Current locust situation
Locust situation 21 April 2020
This page summarises the known distribution of locusts during March and April 2020 and provides a brief outlook to spring 2020. Regional information and forecasts are given in the latest locust bulletin.
Australian Plague Locust (Chortoicetes terminifera)
The locust population level remained generally low in inland eastern Australia during March, but there was a moderate increase from the previous very low numbers in parts of Queensland and New South Wales. This increase indicates background breeding in improved habitat conditions following the sequence of rainfall events since late January. Surveys have been limited because of travel restrictions.
Surveys in Queensland during March identified a small increase in locust population levels in the Central West, South Central and the Central Highlands regions. Adults were recorded at low densities in most areas and low-density, late instar nymphs were identified at two locations in the Central Highlands. Very few adults were identified in Northwest Queensland, where mixed populations of several grasshopper species were recorded at high densities. Fledging of nymphs during March and April is likely to result in moderate increases in adult population levels in several regions.
In New South Wales, adult numbers increased in the Central West and part of the Far West regions during March, following breeding in January and early February. Locusts were reported from the Nyngan and Coonamble areas in early April, but subsequent heavy rainfall prevented access to those areas until mid-April. Surveys identified medium density adults and several small swarms in the Nyngan–Hermidale area and medium densities in the Coonamble–Quambone area. The autumn breeding population has increased to medium densities in parts of the Central West, Far West and Riverina regions. Locust numbers are expected to remain at low densities in other regions.
Previous surveys in South Australia recorded no locusts in the Far North or Northeast regions. Population levels are likely to remain low during the remainder of autumn. Heavy rain in early February and early March in northern regions could have initiated sporadic egg laying, but a large population increase is unlikely during autumn.
No surveys were conducted in Victoria during March. Locusts were reported from north of Bendigo in mid-April, which could represent a more widespread moderate population increase in the North Central region as a result of migrations from New South Wales. However, the overall population level is expected to remain generally low during autumn and spring.
The outlook for the remainder of autumn is for generally low population levels in most regions. Medium density adults will are likely to persist in the Central West and limited areas of the Far West and Riverina regions of New South Wales. Populations in South Australia and Victoria are likely to remain at generally low densities. Egg-laying will continue during April and May. Although a late autumn nymph generation is possible in northern regions of Queensland, the majority of hatchings in other states will be delayed until spring due to diapause and low temperatures.
The spring outlook is for low-density nymphs to develop in several regions of Queensland and New South Wales, with medium and locally high densities possible in parts of Central West, Far West, Riverina and the Northwest Plains of New South Wales. Most hatchings in those regions will occur during September. Summer breeding has produced moderate population increases from low background levels, and a further generation of successful breeding could allow populations to increase to widespread high densities. This would not be possible until after fledging in spring and will depend on environmental conditions in summer. There is a low likelihood of widespread high-density populations during the remainder of autumn, or of region-wide nymph infestations developing during spring.
Spur–throated Locust (Austracris guttulosa)
The summer breeding population level remains very low, but nymphs were recorded at a number of locations in the Queensland Central Highlands in late March.
Surveys in the Northwest and Central West regions of Queensland in mid-March identified very few adults of this species and low-density nymphs at only one location near Muttaburra. Surveys of the Central Highlands and South Central regions in late March identified Isolated density adults. However, low-density nymphs were recorded at a number of locations north of Clermont and also in the Emerald–Springsure and Buckland Plains districts of Central Highlands Regional Council (RC) area. These were the first nymphs detected during 2019–20, although the last surveys of this region were in December. No adults or nymphs were recorded in New South Wales, Victoria or South Australia.The nymphs recorded in the Central Highlands were at various development stages, which indicates that sporadic egg-laying has likely continued since late January in response to repeated periods of heavy rainfall. The few nymphs detected in the northern areas of Central West or Northwest Queensland may reflect the very low numbers of adults in those regions and the high populations of other species, leaving any nymphs below the level of detection. Although this species can lay multiple egg pods, the late arrival of the wet season in Queensland will limit reproductive capacity and nymphs may only develop during March–May. Fledging of nymphs will occur during April and May, and adult numbers could increase to Scattered-Numerous densities in the Central Highlands. This is unlikely to result in a large increase in overall adult population levels. There is a low risk of a widespread infestation developing during autumn or spring 2020.
Migratory Locust (Locusta migratoria)
Adults of this species were recorded at a number of locations during surveys in the Queensland Central Highlands in late March. Isolated–Scattered density adults were identified in the Clermont area of Isaac RC area and at several locations in the Emerald–Rolleston, Arcadia Valley and Buckland Plains districts in Central Highlands RC area. The adults were associated with dense tall grasses along roadsides. No nymphs were identified, but access to less densely vegetated sites was limited. No locusts were recorded during surveys in the Central West and South Central regions of Queensland. However, low numbers were recorded in the Longreach light trap on 23–24 March, indicating that low density populations may be more widespread in Central West Queensland.
The frequency with which this species was detected indicates low-density breeding occurred over a wide area during summer and a significant increase in population in the Central Highlands. It was not identified during previous surveys. Vegetation and soils in locust habitats remain favourable for localised breeding to continue throughout autumn. Gregarization and high-density populations often develop at local scales in habitats such as summer crops.
There is a low risk of a widespread infestation developing during autumn 2020. There is a moderate risk that continued breeding could result in a further population increases and possible localised high-density populations developing during spring 2020.
Locust forecasting regions
Map of forecasting regions with potential locust habitats shaded yellow