Origin and Decline of the 1973 Plague Locust Outbreak in Central Western New South Wales.

1977 ◽  
Vol 25 (3) ◽  
pp. 455 ◽  
Author(s):  
RA Farrow
Keyword(s):  
New South ◽  
New South Wales ◽  
Population Fluctuations ◽  
Green Food ◽  
Synoptic Weather ◽  
South Wales ◽  
Southern Central ◽  
Slow Moving ◽  
And Migration ◽  
Australian Plague Locust

An important outbreak of the Australian plague locust, Chortoicetes terminifera (Wlk.), occurred in 1973 in central western New South Wales. The dynamics of the outbreak could be resolved into a sequence of five principal interacting events: (1) Sustained population increases in low-density populations in northern central western New South Wales during three successive breeding periods in 1972. The increases were a result of successful, local multiplication, immigration from more northerly breeding areas and restricted opportunities for dispersal. The continuing concentration of locusts in the northern central west led to local gregarisation and swarm formation in autumn and spring 1972. (2) Massive southward displacements at night during an intense tropical disturbance between 29 January and 4 February 1973, which resulted in an invasion and concentration of infestations in southern central western New South Wales. (3) Substantial multiplication increases (10- to 30-fold), as a result of the drought-breaking rainfall in the autumn and spring of 1973 in the central-west. This resulted in an intensification of the plague with the production of numerous, slow-moving swarms. (4) Massive southward displacements during several periods of disturbed weather in spring 1973, which led to the disappearance of adult infestations from the central west and a dispersal of infestations in areas invaded further south. (5) Heavy mortality in residual populations of hoppers and eggs. The combined effects of parasites, predators and a reduced viability of eggs and hoppers resulted in a complete collapse of the plague in the central west by December 1973.Although displacement by adults at night is shown to be the principal factor regulating both population fluctuations in specific localities and the spread of plagues through southward invasions, outbreaks are ultimately determined by initial multiplication increases in relatively sedentary recession populations. Both multiplication and migration were influenced more by variations in synoptic weather than by any other factor. Diurnal swarm movements, although conspicuous, did not significantly influence the overall spread of the outbreak studied.The quality and quantity of available fresh green food did not appear to limit further successful breeding during the decline of the plague. Although influxes of locusts into the central-west continued during disturbed weather in 1974, none remained to breed and densities fell to levels (<1/ha) lower than those of drought seasons. It appears unlikely, therefore, that plagues can be sustained in any one area, even when environmental conditions remain favourable for breeding, because of: (1) mass emigration during disturbed weather; (2) increased effectiveness of natural enemies; and (3) declines in viability and fecundity in moist conditons.

Population Dynamics of the Australian Plague Locust, Chortoicetes Terminifera (Walker), in Central Western New South Wales. I. Reproduction and Migration in Relation to Weather.

1979 ◽  
Vol 27 (5) ◽  
pp. 717 ◽  
Author(s):  
RA Farrow
Keyword(s):  
New South ◽  
New South Wales ◽  
Population Fluctuations ◽  
Relative Importance ◽  
Net Migration ◽  
South Wales ◽  
Reproductive Rates ◽  
And Migration ◽  
Australian Plague Locust

On three adjacent experimental plots in central western New South Wales, from 1971 to 1974, population fluctuations of the Australian plague locust were interpreted in terms of the interactions between reproductive rates (Ro) between generations and net migration losses or gains (M plus or minus ) within generations. Changes due to variations in net migration fluctuated over a greater range than those due to variations in reproductive rates, and were the major cause of the population fluctuations during the 16 generations studied. Variations in rainfall during breeding accounted for nearly 90% of the variance in reproductive rates, provided rain followed relatively dry periods. Changes caused by migration resulted from episodic, often long-range and generally southward displacements of adults at night in the gradient wind during disturbed weather. The frequency and intensity of migration depended primarily on the availability of potential emigrants and secondarily on the incidence of weather favourable for takeoff and prolonged flight. The incidence of rainfall before periods of migration was higher than expected. Adults thus migrated into areas already favourable for successful breeding. Long-term median rainfall during breeding at Trangie gave mean reproductive rates greater than 1 per generation. Hence, population surpluses tend to be produced and generally disperse south to areas less favourable for breeding. There was close correspondence between the occurrence of heavy drought-breaking rains, leading to substantial population increases and migrations, and the observed incidence of outbreaks in this area. Changes in the relative importance of reproduction and migration in the drier breeding areas further inland are discussed in relation to historical changes in the distribution and abundance of the plague locust.

Population Dynamics of the Australian Plague Locust, Chortoicetes Terminifera (Walker) in Central Western New South Wales. Ii. Factors Influencing Natality and Survival.

1982 ◽  
Vol 30 (2) ◽  
pp. 199 ◽  
Author(s):  
RA Farrow
Keyword(s):  
Biological Control ◽  
Population Dynamics ◽  
Natural Enemies ◽  
New South ◽  
New South Wales ◽  
Development Stages ◽  
Factors Influencing ◽  
South Wales ◽  
Savannah Woodland ◽  
Australian Plague Locust

Unrealized natality and mortalities at successive development stages were measured during synchronized breeding by populations of the Australian plague locust. Studies were made over a 3-y period, covering nine generations, on small plots situated in pastures derived originally from savannah woodland in central western New South Wales. Variations in natality and mortalities were influenced more by variation in soil moisture, primarily through its effect on pasture conditions, than by the effects of natural enemies; these variations were closely correlated with seasonal rainfall. Unidentified losses, independent of known variables, were recorded in the hopper stage and were highest in the hatchling. Such losses invariably exceeded 60% even under the most favourable conditions encountered in the field during the study period. The quantitative relationships established in this study between the plague locust and its natural enemies and other environmental factors suggest that prospects for the biological control of this pest by either native or introduced species are poor.

Migrating moths collected in tower-mounted light traps in northern New South Wales, Australia: influence of local and synoptic weather

1994 ◽  
Vol 84 (1) ◽  
pp. 17-30 ◽  
Author(s):  
P.C. Gregg ◽  
G.P. Fitt ◽  
M. Coombs ◽  
G.S. Henderson
Keyword(s):  
Relative Humidity ◽  
New South ◽  
New South Wales ◽  
Early Summer ◽  
Pest Species ◽  
Light Traps ◽  
Long Distance ◽  
Forest Zone ◽  
Synoptic Weather ◽  
South Wales

AbstractCatches of moths in tower-mounted light traps in northern New South Wales were analysed in relation to local and synoptic weather. Catches were correlated with windspeed, relative humidity and possibly rainfall. No correlations were obtained with temperature or moon phase. Catches were more likely to occur when winds were from the east, and were associated with wind shifts. There was a significant association with the passage of depressions or troughs, but not cold fronts. The traps were considered to be poor indicators of migration associated with fronts, because these were accompanied by high winds in which trap efficiency was reduced. Stepwise multiple regressions using temperature, relative humidity, rainfall and windspeed accounted for only about 25% of the variance, much lower than in comparable studies with ground level light traps. These results are thought to indicate that the trap catches were reflecting long-distance migration, which was usually associated with disturbed weather. Back tracking with upper wind data was used to define probable sources of moths. In the spring and early summer, these sources were predominantly to the north and west of the traps, in semi-arid pastoral and subhumid cropping zones. In the late summer and autumn they were predominantly to the south and east, in the humid pastoral and forest zone. These results are discussed in relation to the migratory strategies of several important agricultural pest species.

History of outbreaks of the Australian plague locust, Chortoicetes terminifera (WALK.) between 1933 and 1959, and analysis of the influence of rainfall on these outbreaks

1962 ◽  
Vol 13 (4) ◽  
pp. 674 ◽  
Author(s):  
M Casimir
Keyword(s):  
Multiple Regression ◽  
New South ◽  
New South Wales ◽  
Regression Equations ◽  
Relative Significance ◽  
Early Season ◽  
South Wales ◽  
Outbreak Areas ◽  
History Of ◽  
Australian Plague Locust

An account of the history of outbreaks of the Australian plague locust, Chortoicetes terminifera, is presented for the period 1933–1959 from published information and records maintained by the New South Wales Department of Agriculture. Population fluctuations during this period have been examined in relation to rainfall for seven of the major and intermediate outbreak areas in New South Wales. It has been shown that rainfall during the months August to December is important in its influence on locust numbers the following season, whereas that occurring between January and April is apparently not. Subnormal "early season" rainfall favours an increase in the locust population of an area in the next season, while above-normal rainfall favours a locust decrease in the following season. In each of the outbreak areas selected there was a significant negative correlation between the current first locust generation of the season (measured in terms of an arbitrary scale or index) and preceding early season rainfall; and the estimated regression lines due to the two variables in each area were apparently parallel, although not coincident. A multiple regression analysis was carried out incorporating the preceding autumn locust generation as an extra independent variable. When the Culgoa-Barwon outbreak area was eliminated from the analysis, it was found that the regression equations for each of the six other areas could be considered identical, even to the constant term, any differences between areas being attributable to differences in the values of the independent variables. A single multiple regression equation based on the data for the six areas combined was calculated, and it is suggested that this can be used to forecast approximately the size of the spring locust generation in time to plan appropriate control measures. Difficulties inherent in the data are pointed out and the disturbing influence of invasion of one area by migrating swarms from another discussed. It is believed that more refined methods of estimating locust numbers and greater knowledge of locust behaviour in relation to long-term rainfall influences would allow predictions of much greater accuracy to be made, based on the correlations established in the present paper. The relative significance of outbreak areas situated mainly in the Central Division of New South Wales and those in far western parts of New South Wales and Queensland is discussed. It is suggested that two of the most serious outbreaks on record were the result of long-range migratory flights from the latter areas. The importance of these areas as a source of outbreaks affecting South Australia, Victoria, and southern New South Wales is also emphasized, and a tentative explanation of the role of early season rainfall in these arid regions is given.

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