This page summarises the known distribution of locusts during April and provides a brief outlook to spring 2015. Regional information and forecasts are given in the latest locust bulletin.
The adult locust population declined to low densities in most regions during April. Only low numbers were identified in Southwest and Central West Queensland, and in Far West New South Wales. Similar low densities are now likely to be in South Central and Central West Queensland, Northwest New South Wales and the Far North and Northeast regions of South Australia. Residual medium–high density adults and nymphs persisted in the eastern part of Central West New South Wales after several generations of high density local breeding. Medium density adults also remained in limited parts of the southern Riverina and Northwest Victoria as a result of migrations in March. These are the most significant known areas for autumn breeding, where medium and some localised high density nymphs are likely to develop in spring. Breeding in other regions is likely to have been at low densities. No further significant long-distance migration was detected during April.
In Central West New South Wales, adult numbers declined in the infested areas around Gilgandra–Baradine–Coonamble and Coonabarabran–Mendooran–Binnaway–Dunedoo during April, but sporadic swarm egg laying continued in these areas in March and early April. Nymphs will appear during September, with the likely development of localised high densities and some bands. Adults persisted in the Deniliquin–Wakool area of the Riverina in mid-April and egg laying there is likely to produce medium and possibly some high density localised nymphs from early October. Sporadic hatchings are also possible in the Narrabri, Tamworth, Armidale and Barraba districts of the Northwest Plains.
The decline in adult densities continued in all regions of Queensland during April. Surveys by APLC and Biosecurity Queensland staff detected only low density adults in the Southwest, Central West and South Central regions. Localised nymphs that developed in the Maranoa and Western Downs Regional Council areas in March will have fledged during April, but no population increase was reported.
Adult densities will have declined to low density in Far North and Northwest South Australia, after migration in mid-March. A resulting small increase in population density was identified in the southern Flinders Ranges districts, but there was no detectable change in the Murray Valley region. Rainfall during April in these regions has provided suitable vegetation and soil conditions for sporadic egg laying by this low density population, which could produce some nymphs at low densities during spring.
Following some immigration into northern Victoria during March, surveys detected only a small population increase. However a number of reports were received from the Wimmera and Mallee districts in mid-April and Department of Economic Development staff identified medium density gravid adults at several locations. Egg laying by these adults could produce localised low and medium density nymphs in October.
The spring outlook is for some localised development of nymphs in the Central West, Northwest and southern Riverina regions of New South Wales, Northwest Victoria and South Central Queensland. Localised high densities and some small bands are likely in New South Wales, while mostly low densities are expected in the other regions. The majority of eggs laid during March and April will remain dormant during winter and hatch in spring. Hatching will commence in late August in southern Queensland, early September in Central West New South Wales and mid-October in Victoria. There is a low risk of more widespread regional infestations developing in spring.
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, Southwest and South Central Queensland during March and April, as recently fledged adults aggregated and formed small roosting swarms in some areas. Similar increases are likely to have occurred in the Northwest and Gulf regions of Queensland. Adults were recorded at swarm density at several locations in the Central Highlands and Central West Queensland during March. Biosecurity Queensland received several swarm reports from the Central Highlands and carried out limited swarm control east of Dysart in late March.
The overwintering adult population level will not increase significantly during winter, as the majority of nymphs produced by summer breeding have now fledged. However, young adults will continue aggregating to form swarms, which will persist during winter, and could cause localised crop and tree damage. Localised 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 occasional, largely sedentary swarms persisting throughout winter in parts of these regions. The increase in population this year, compared to recent years, resulted from repeated successful breeding during summer. Some swarm movement and migrations are possible during spring, but only a small number of swarms are likely to affect agricultural areas.
Medium and high densities of this species persisted in the Queensland Central Highlands during April. Biosecurity Queensland conducted aerial control of swarms covering a total area of 20,000 ha in the Emerald and Clermont areas in early April. Swarms were also reported in Banana Shire in mid-April. Several swarms were identified in the Blackall–Yalleroi area of Central West Queensland in late March and occasional adults were recorded in the Longreach area.
Several periods of moderate–heavy rainfall during March maintained suitable habitat conditions for continued breeding. However, there was only localised moderate (20–40 mm) rainfall in mid-April, which may restrict further breeding opportunities. This species is capable of producing multiple generations and continuous breeding in favourable conditions, although any breeding activity during winter will be limited. Gregarisation can occur at local scales, often associated with cropping in eastern Queensland, and can therefore be difficult to detect without intensive surveys. Landholders are encouraged to report swarms, egg laying or hatchings. There is a moderate probability of small gregarious populations persisting in the Central Highlands region during winter.