Locust Bulletin October 2019

The locust population level remained low over most inland regions of eastern Australia throughout 2018-19. Only sporadic low density breeding occurred, maintaining the overall low population densities. Vegetation in most areas that received rainfall during summer dried out rapidly and habitats became increasingly dry in autumn. Low food availability combined with prolonged high temperatures are likely to have contributed to increased mortality of nymphs and adults.

Heavy flood rains (>100 mm) in western Queensland during February and March produced habitat conditions suitable for locust breeding. Floodwaters moved down the channels of the Thompson, Diamantina and Georgina rivers and the Eyre Creek during March and April, extending the vegetation response southwards in late autumn and winter. Surveys in western Queensland in April and May 2019 identified a moderate increase in adult numbers over preceding months and low density nymphs were recorded in some locations of the Southwest and Northwest regions. Subsequent surveys of these regions during September recorded a similar population level. Low density adults were widespread, but most were recently fledged from a winter nymph generation. Localised medium density adults and residual low density late-instar nymphs were identified in the Windorah area. Vegetation remained green in flood-out areas during winter, but was becoming dry in most areas by September.

Surveys recorded very few locusts in the Riverina, Central West and Northwest Plains regions of New South Wales in late autumn. Low density adults were identified in the Tibooburra and Bourke districts of the Far West region in May, representing a small increase in numbers over preceding months. Late autumn rainfall in parts of the Far West and Far Southwest and Riverina regions produced green vegetation during winter, which became dry during September. September survey of the Far Southwest region recorded only occasional adults. There have been no reports from the Central Tablelands or Hunter regions, despite locust populations developing in those areas in summer.

Surveys in South Australia over the previous summer and autumn recorded very few locusts. Survey of the Northeast region in late September did not detect any locusts. Habitat conditions are green in southern regions but remain very dry in the northern half of the state.

In Victoria, locust numbers remained very low in inland areas during autumn. Habitat conditions have improved after winter rainfall, but the locust population is likely to remain at low densities during spring. Some nymphs could develop during spring from eggs laid by the local population in the Omeo Valley area of East Gippsland.

The spring outlook is for continuing low population densities in most regions of inland eastern Australia. Drought conditions across much of New South Wales, South Australia and Queensland have resulted in very low locust population levels and unfavourable habitat conditions. It is likely that more than one generation of successful breeding would be necessary to produce large population increases. The Bureau of Meteorology seasonal outlook indicates that below average rainfall and above average temperatures are likely to continue over coming months. Therefore there is a low likelihood of high density populations developing in any inland region during spring.

There is a very low probability of widespread regional infestations developing in spring or December.

2 October 2019

The population level of this species remained very low throughout 2018-19. Only low density adults were recorded by surveys in Queensland and no nymphs were detected. Very few adults were recorded in New South Wales or South Australia. This was one of the smallest annual populations recorded in APLC survey regions and is likely be the result of a low summer breeding population base and the late and sporadic wet season rainfall over the last two years.

The heavy rainfall in the Northwest, Central West and Gulf regions of Queensland during autumn provided suitable habitat for autumn breeding. However, surveys during April and May in Northwest and Central West Queensland recorded only low density adults and no nymphs were detected. Locust habitats in the Queensland Central Highlands remained mostly dry during summer and autumn. Nymphs and eggs are susceptible to desiccation and high mortality can occur in dry habitat conditions.

Surveys of Southwest and parts of Northwest Queensland in early September recorded Isolated density adults in areas associated with residual green vegetation from the flooding during autumn.

There is a low risk of a widespread infestation developing during spring 2019 or summer 2020.

Adult locusts were recorded at very low density in a few locations in Southwest and Central West Queensland, and north of Clermont in the Central Highlands during May. Habitat conditions have become mostly dry in areas where this species was detected.

There is a low risk of a widespread infestation developing during spring or December 2019.

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Locusts and conditions

• Locust population density declined to very low levels during autumn, after a moderate increase in adult population level in eastern Central West and Northwest Local Land Services (LLS) regions in February. Surveys in May recorded no locusts in the Northwest and only occasional adults in the Coonamble–Quambone district of Central West LLS.
• There were no further locust reports after February from the areas in the northern Central Tablelands and Hunter LLS areas where locusts developed during summer.
• There was moderate rainfall (20-40 mm) in the eastern Central West and Northwest LLS regions, and heavy rainfall (>40 mm) in the Central Tablelands and Hunter LLS during March. There were further moderate falls during May and only light rainfall (<20 mm) in the Northwest and Central West LLS regions during winter. Habitat conditions are now dry in most areas of Northwest and Central West LLS regions. There was light–moderate rainfall in parts of the Central Tablelands and Hunter LLS regions in mid-September.

Forecast

• The locust population is expected to remain at a low level in these regions during spring.
• Spring hatchings will have commenced in early September in Northwest LLS and in mid-September in Central West and Central Tablelands LLS. Only localised low density nymphs are likely to develop in Central West and Northwest LLS regions.
• Areas of the northern Central Tablelands and Hunter LLS regions where locusts were reported in early 2019 received heavy rainfall in March. This would have provided suitable habitat conditions for autumn breeding. Nymphs are likely to develop in some areas during October, mostly at Present–Numerous densities. High density nymphs are possible in restricted locations, but survival may be limited by food availability in dry habitats.
• The likelihood of significant breeding during November or December will be influenced by the distribution of rainfall during those months.
• There is a very low probability of any locust immigration during spring.

Risks

• There is a low risk of a widespread regional infestation developing during spring or December.

Locusts and conditions

• The locust population declined to very low numbers during autumn. Surveys in autumn recorded no locusts and habitat conditions were very dry in most areas.
• There was moderate–heavy rainfall (20->40 mm) across the southern Riverina during May and further patchy light falls during winter. Pasture vegetation was green in these areas during August, but became dry during September.

Forecast

• Locust numbers are likely to remain at a low level during spring, given the very low prior population and limited breeding opportunities.
• Any spring hatchings will have commenced in late September in the Riverina LLS and early October in Murray LLS. Nymph survival will be limited by dry habitat conditions in the absence of moderate–heavy rainfall during spring.
• There is a very low probability of immigration from other regions during spring.

Risks

• There is a low risk of a widespread infestation developing during spring or December.

Locusts and conditions

• There was a small increase in population density during May in the Far West region from the very low numbers recorded during summer and early autumn. Very few locusts were recorded in the Far Southwest region during May.
• September survey in part of the Far Southwest region identified only occasional adult locusts in the Ivanhoe district.
• The Fowlers Gap and White Cliffs light traps recorded no locusts during September.
• There was moderate–heavy rainfall (20->40 mm) in the Wanaaring, Wilcannia, Cobar and Ivanhoe districts during April. Pasture vegetation was green in these areas during winter, but became dry in September.

Forecast

• Locust numbers are likely to remain low during spring, given the very low current population level and ongoing dry habitat conditions in most areas.
• Only very low density egg laying was possible during autumn in most areas and only occasional nymphs are expected in spring.
• Spring hatching would have commenced in late August in the Far West and mid-September in the Far Southwest. Nymph survival will be limited by poor habitat conditions.
• There is a very low probability of significant immigration from other regions during spring.

Risks

• There is a low risk of a widespread infestation developing during spring or December.

Locusts and conditions

• The locust population level remained generally low in areas surveyed during May, despite widespread heavy rainfall during autumn. Autumn breeding maintained the low overall population densities during winter and widespread low density adults were recorded in September.
• Surveys during May identified Isolated–Scattered density adults in many areas of Barcoo, Bulloo and Diamantina shires. Scattered-Numerous density adults and low density nymphs over a range of instar stages were recorded in the Windorah–Warbreccan area. Only isolated density adults were recorded in Quilpie Shire.
• Surveys during September identified similar adult densities, but most had recently fledged from a winter nymph generation. Isolated–Scattered density adults were recorded in all shires, with Scattered–Numerous density adults and occasional residual late-instar nymphs in the Windorah area.
• No locusts were recorded Nooyeah Downs light trap during September. The Birdsville light trap is currently not operating.
• There was widespread heavy rainfall (40-200 mm) during March and further moderate–heavy rainfall (20->40 mm) in Bulloo Shire in April. Floodwaters passed down the Cooper Creek and Diamantina River, resulting in floodplain vegetation growth during autumn. There has been no significant rainfall since May. Vegetation is now dry in most areas.

Forecast

• Locust numbers are expected to remain low during spring, given the current low population level and drying habitats. Only sporadic, low density egg laying occurred during late autumn and nymphs developed during winter. There is therefore unlikely to be any significant spring hatching.
• Only low density breeding is likely during spring, largely restricted to areas near residual green vegetation. Nymph survival will be limited without moderate–heavy rainfall, which is unlikely before November.
• There is a low probability of immigration from other regions during spring.

Risks

• There is a low risk of a widespread infestation developing during spring or December.

Locusts and conditions

• The locust population level was low in areas surveyed in late autumn, despite widespread heavy rainfall producing favourable habitat conditions for breeding. Population numbers remained low during September.
• Surveys during May identified Isolated–Scattered density adults and occasional low-density nymphs in Winton Shire and Longreach Regional Council (RC) area. Only occasional Isolated density adults were recorded in Boulia Shire.
• Surveys during September identified Isolated-Scattered density adults in Boulia and western Winton shires.
• No locusts were recorded at the Longreach light trap during September.
• There was widespread heavy rainfall (>40 mm) during March and further moderate rainfall (20-40 mm) in Tambo RC area in April. Vegetation remained green in some areas during winter, but is now dry in most areas.

Forecast

• Locust numbers are likely to remain low during spring, given the low background population level and drying habitats.
• The survival of any nymphs during spring will be limited without moderate–heavy rainfall, which is unlikely before November.
• There is a low probability of significant immigration from other regions during spring.

Risks

• There is a low risk of a widespread infestation developing during spring or December.

Locusts and conditions

• The locust population is expected to have remained generally low during September.
• Surveys during May identified only occasional Isolated density adults in the Emerald area.
• There was widespread heavy rainfall (>40 mm) during March and light–moderate rainfall (<20-40 mm) during April. There was further patchy light rainfall (<20 mm) during June and July. Vegetation remained green in some areas during winter, but is becoming dry in most areas.

Forecast

• The locust population level is likely to remain generally low during spring. Only sporadic low-density breeding was possible in autumn, given the very low background population.
• Any autumn egg laying would have resulted in hatchings during September, but nymphs are only likely to develop at low density.
• There is a very low probability of any immigration from other regions during spring.

Risks

• There is a low risk of a widespread infestation developing during spring or December.

Locusts and conditions

• The locust population level remained very low in these regions during May and there were no reports of locust activity during August or September.
• Surveys during May recorded no locusts in Western Downs or Goondiwindi RC areas. Only occasional Isolated density adults were identified in Paroo, Murweh and Balonne shires.
• There was moderate–heavy rainfall (20->40 mm) in Paroo and Murweh shires during April. There was no significant rainfall in these regions during winter or September. Pasture vegetation is very dry in most areas.

Forecast

• The locust population is likely to remain very low during spring, after ongoing drought conditions and very low prior population densities. Opportunities for breeding will be limited without moderate–heavy rainfall during spring.
• Any autumn laid diapause eggs would have hatched in early September or remain in quiescence in dry soils.
• There is a low probability of immigration from other regions during spring.

Risks

• There is a low risk of a widespread infestation developing during spring or December.

Locusts and conditions

• Locust population densities remained very low during summer and autumn 2019. There were no reports of locust activity during September.
• September of the survey in the Hawker–Burra area of the Northeast region did not detect any locusts, despite spring pasture growth south of Orroroo.
• The Dulkaninna light trap did not record any locusts during September. The Oodnadatta light trap is currently not operating.
• There was light-moderate (<20-40 mm) rainfall in southern parts of the Western Agricultural and Northeast regions during May and June. There was light–moderate rainfall in part of the Western Agricultural region during 15-12 September. Ground vegetation is green in the southern Northeast and Western Agricultural regions, but remains very dry in the northern half of the state.

Forecast

• The locust population is likely to remain at very low level density during spring.
• The current very low background population and ongoing drought conditions in will limit any opportunities for breeding in the Far North and Northwest regions. Habitat conditions favour the survival of any nymphs on the Eyre Peninsula, but this is unlikely to result in a large population increase.
• There is a low probability of migrations into these regions during spring.

Risks

• There is a low risk of a widespread infestation developing during spring or December.

Locusts and conditions

• Locust densities remained very low in these regions during autumn. There were no reports of locust activity during September.
• These regions received light–moderate rainfall (<20-40 mm) each month since May, with some totals > 50 mm in southern areas. Spring pastures remain green in some southern areas.

Forecast

• The locust population level is likely to remain very low during spring.
• Only sporadic low-density breeding was possible in autumn, given the very low background population.
• Any hatching of autumn diapause eggs will commence in early October.
• Habitat conditions favour the survival of any nymphs in the Southeast region and part of the Murray Valley, but this is unlikely to result in a population increase.
• There is low probability of any immigration from other regions during spring.

Risks

• There is a low risk of a widespread infestation developing during spring or December.

Locusts and conditions

• The locust population level remained very low during autumn and no reports were received during September.
• No surveys were conducted and there were no reports of locust activity during September.
• There have been no reports from the Omeo–Swifts Creek area since February.
• Much of Victoria received moderate–heavy total rainfall (20->40 mm) during May, June and July. There was further patchy light rainfall during the first week of September. Pasture vegetation is green in southern areas of the state.

Forecast

• Locust numbers are likely to remain very low in inland areas during spring, given the very low background population. Sporadic autumn breeding will produce only low density nymphs.
• Spring hatching will commence in early October in northern Victoria and from mid-October in the southern half of the state.
• The persistent locust population in the Omeo Valley could develop again during spring from autumn-laid eggs. Diapause eggs will hatch during October and localised low-medium density nymphs could develop in some areas.
• There is a low probability of significant immigration from other states during spring.

Risks

• There is a low risk of a widespread infestation developing during spring or December.

Locust biology and behaviour

Where higher densities occur, a large proportion of the regional population is concentrated in very small areas with lower densities elsewhere, so the higher densities cannot be extrapolated over the area of an entire region. A range of density classes is usually found within a surveyed region.

It is important that all locust activity is reported as soon as possible to your nearest state agriculture agency office or to the Australian Plague Locust Commission.

Reports to the Australian Plague Locust Commission can be made by:

Free call (Canberra): 1800 635 962 (24 hours)
Fax (Canberra): (02) 6272 5074
E–mail: APLC
Internet: Australian Plague Locust Commission