Locust Situation 3 April 2015
This page summarises the known distribution of locusts during March and provides a brief outlook to spring 2015. Regional information and forecasts are given in the latest locust bulletin.
Australian Plague Locust (Chortoicetes terminifera)
A widespread, medium–high density adult population persisted in several regions of Queensland and New South Wales during March, with small swarms recorded in parts of South Central, Central West and Southwest Queensland, and in Central West and Far West New South Wales. A general decline in swarm numbers and densities was detected in these regions in late March. Nocturnal long distance migrations in mid-March resulted in small increases in adult densities in northern Victoria, the southern Riverina and Northeast South Australia, as well as reports from some eastern districts of New South Wales. Nymph bands developed in the eastern half of Central West New South Wales and in a localised area of South Central Queensland following egg laying during February, and landholders continued to carry out control in these areas. These nymphs and those that fledged in Far West New South Wales and Far North South Australia in early March represent the third nymphal generation, which developed at only low densities in other regions due to the absence of widespread heavy rainfall during February.
In Central West New South Wales, swarms persisted in the Gilgandra–Baradine–Coonamble and the Tooraweenah–Coonabarabran–Binnaway areas during the first half of March. Swarms spread to the Dubbo, Mendooran and Dunedoo areas, where both egg laying and hatching were reported throughout March. A few swarms and nymphs were also reported from the Tamworth, Armidale and Barraba areas in the Northwest Plains. Fledging of nymphs in the Fowlers Gap–Tibooburra area of the Far West region in early March produced high density adults and a few swarms, but migration to the south-east contributed to a subsequent decline numbers and an increase in the southern Riverina.
High density adults and swarms persisted in Southwest and Central West Queensland during the first half of March, but a gradual decline in numbers was detected by the end of the month. Nymph Bands developed in the Roma–Surat area of South Central Queensland from early March and fledging will occur in April. Dry conditions limited the opportunities for swarm egg laying in the Southwest and Northwest regions, but rainfall in the eastern Central West is likely to have initiated sporadic egg laying by swarms remaining in the Barcaldine and Blackall-Tambo Regional Council areas.
Fledging of the February nymph generation in the Far North of South Australia produced increased adult densities in early March. Southward migration in mid-March resulted in a small increase in population density in the southern Flinders Ranges districts, but no detectable change in the Murray Valley region.
Immigration into northern Victoria was detected on 18 March. However, subsequent surveys of the Northwest region indicated only a small increase in overall numbers and a low risk of widespread egg laying.
The autumn outlook is for a continued decline in adult population level in most regions. The localised high density nymphs in Central West New South Wales and South Central Queensland will fledge during April, and could produce some minor swarm activity. Nymphs could develop in part of Central West Queensland during April. Migrations that occurred in mid-March present a low risk of widespread spring infestations to Victoria, South Australia or southern New South Wales. Further minor migrations are possible during April. The majority of eggs laid during April will enter diapause and hatch in spring. Localised nymph infestations are likely to develop in Central West New South Wales and South Central Queensland during September–October.
Spur–throated Locust (Austracris guttulosa)
There is a widespread medium density population of young adults in regions of inland Queensland. Adult densities increased in parts of the Central Highlands, Central West, Northwest, Southwest and South Central Queensland as fledging of nymphs from summer breeding continued and recently fledged adults aggregated to form roosting swarms in some areas. Similar increases are likely to have occurred in the Northwest and Gulf regions. Adults were recorded at Concentration and swarm density at several locations in the Central Highlands and Central West Queensland. Biosecurity Queensland received several swarm reports and carried out limited swarm control east of Dysart in late March.
Surveys in March recorded Scattered–Numerous density adults and occasional low density nymphs in the Longreach, Barcaldine, Blackall-Tambo, Isaac, Central Highlands and Maranoa Regional Council (RC) areas. Previous surveys of the Northwest and Southwest regions identified widespread Scattered–Numerous density young adults and medium density nymphs in Winton, Boulia, McKinlay, Richmond, Barcoo, Cloncurry, Diamantina Shires. Lower numbers were recorded in Bulloo, Quilpie, Paroo and Balonne Shires, and only occasional adults in other States.
The overwintering adult population level will not increase significantly after April, as the bulk of this generation has now fledged. However, young adults will continue aggregating to form swarms in autumn, often roosting in woodland areas during winter and causing localised crop and tree damage. Further swarm formation is likely in parts of the Central Highlands, Central West and Northwest Queensland. Similar populations are also likely in the Queensland Gulf and some regions of the Northern Territory. There is a moderate risk of some largely sedentary swarms persisting throughout winter in parts of these regions. Young adults can migrate during autumn and small increases in numbers could therefore occur in other regions. The increase in population this year, compared to recent years, resulted from repeated successful breeding during summer. Some sampled adults in March still showed egg development, indicating that multiple egg pods could have been laid by previous generation females.
Migratory Locust (Locusta migratoria)
APLC surveys in early March identified Numerous density adults at a number of locations in the Avon Downs–Clermont–Capella area of Isaac RC area, along with a band of mid instar nymphs near Kilcummin. In Central Highlands RC area, consistent Numerous density adults were identified in the Emerald–Springsure area and Numerous–Concentration densities in the Buckland Plains area to the south-west. In the South Central region, Isolated–Scattered density adult were recorded in the Mitchell–Injune, Morven–Moorak and Charleville–Langlo Crossing areas, and in the Central West there were Scattered to Numerous densities in the Tambo–Mt Playfair and Barcaldine–Aramac–Jericho areas. In late March, several swarms were identified in the Blackall–Yalleroi area and sampled females were developing eggs. Occasional adults were also identified in the Longreach RC area.
Several periods of moderate–heavy rainfall during March have maintained suitable habitat conditions for continued breeding. This species is capable of producing multiple generations and continuous breeding in favourable conditions, which can produce regional populations where all lifestages are present. Gregarisation can occur at local scales, often associated with cropping in eastern Queensland, and can therefore be difficult to detect without intensive surveys. There is a moderate probability of further localised gregarious population developments and of an infestation in the Central Highlands region continuing into winter.