Edward Deveson

Challenges to assessing connectivity between massive populations of the Australian plague locust

Linking demographic and genetic dispersal measures is of fundamental importance for movement ecology and evolution. However, such integration can be difficult, particularly for highly fecund species that are often the target of management decisions guided by an understanding of population movement. Here, we present an example of how the influence of large population sizes can preclude genetic approaches from assessing demographic population structuring, even at a continental scale. The Australian plague locust, Chortoicetes terminifera, is a significant pest, with populations on the eastern and western sides of Australia having been monitored and managed independently to date. We used microsatellites to assess genetic variation in 12 C. terminifera population samples separated by up to 3000 km. Traditional summary statistics indicated high levels of genetic diversity and a surprising lack of population structure across the entire range. An approximate Bayesian computation treatment indicated that levels of genetic diversity in C. terminifera corresponded to effective population sizes conservatively composed of tens of thousands to several million individuals. We used these estimates and computer simulations to estimate the minimum rate of dispersal, m, that could account for the observed range-wide genetic homogeneity. The rate of dispersal between both sides of the Australian continent could be several orders of magnitude lower than that typically considered as required for the demographic connectivity of populations.

Modeling spatiotemporal dynamics of outbreaking species: influence of environment and migration in a locust

Many pest species exhibit huge fluctuations in population abundance. Understanding their large-scale and long-term dynamics is necessary to develop effective control and management strategies. Occupancy models represent a promising approach to unravel interactions between environmental factors and spatiotemporal dynamics of outbreaking populations. Here, we investigated population dynamics of the Australian plague locust, Chortoicetes terminifera, using density data collected between 1988 and 2010 by the Australian Plague Locust Commission over more than 3 million km2 in eastern Australia. We applied multistate and autologistic multi-season occupancy models to test competing hypotheses about environmental and demographic processes affecting the large-scale dynamics of the Australian plague locust. We found that rainfall and land cover predictors best explained the spatial variability in outbreak probability across eastern Australia. Outbreaks are more likely to occur in temperate than tropical regions, with a faster and more continuous response to rainfall in desert than in agricultural areas. Our results also support the hypothesis that migration tends to propagate outbreaks only locally (over distances lower than 400 km) rather than across climatic regions. Our study suggests that locust outbreak forecasting and management systems could be improved by implementing key environmental factors and migration in hierarchical spatial models. Finally, our modeling framework can be seen as a step towards bridging the gap between mechanistic and more phenomenological models in the spatial analysis of fluctuating populations.

Satellite normalized difference vegetation index data used in managing Australian plague locusts

Abstract The Australian Plague Locust Commission (APLC) has a mandated role in monitoring, forecasting, and managing populations of key locust species across four Australian states. Satellite normalized difference vegetation index (NDVI) imagery is used to monitor vegetation condition in locust habitat and is integrated with mapping software to support forecasting and operations within the strategic framework of APLC activities. The usefulness of NDVI data for monitoring locust habitats is tested using historical control and survey records for the Australian plague locust, Chortoicetes terminifera (Walker). In arid habitat areas, control of high-density nymphal populations was consistently associated with high and increased relative NDVI during summer and autumn, providing important information for locating possible infestations. Regression models of NDVI data and regional biogeographic factors were fitted to summer survey records of C. terminifera presence and abundance. Models identified increased vegetation greenness, measured by a one-month positive change in NDVI, as having a significant positive relationship with nymph distributions, while NDVI was significant in adult distributions. Seasonal rainfall regions and a binary habitat stratification were significant explanatory factors in all models.

Naturae Amator and the Grasshopper infestations of South Australia's early years

Abstract The descriptions of the natural history of south Australia written by Charles Algernon Wilson (Naturae Amator, Delta) from 1841 to 1845 reveal much about the romantic vision of a young naturalist in an unknown southern world as he savoured the unlimited prospects of the new colony. They also provide sufficient detail about the grasshoppers that became an annual swarming pest around Adelaide during 1843–1848 to assign it to the common species Austroicetes cruciate (saussure 1888). This resets the early history of grasshopper and locust outbreaks in Australia, where the first reports in south Australia have been attributed to the Australian plague locust, Chortoicetes terminifera (Walker, F. 1875). It also introduces the possibility that the swarms resulted from early ecological changes brought about by the introduction of European livestock and agriculture to this continent.

Embryonic diapause in the Australian plague locust relative to parental experience of cumulative photophase decline

The Australian plague locust Chortoicetes terminifera (Walker) exhibits facultative embryonic diapause during autumn. To approximate natural photoperiod changes during late summer and autumn, locust nymphs were reared under different total declines in laboratory photophase (-0.5, -0.75, -1.0, -1.25, -1.5, -1.75, -2 h each lowered in 15 min steps) in a 24 h photoperiod to quantify any effect on the subsequent production of diapause eggs. Induction of diapause eggs was significantly affected by accumulated photoperiod decline experienced by the parental generation throughout all development stages from mid-instar nymph to fledgling adult. The incidence of embryonic diapause ranged from nil at -0.5 h to 86.6% diapause at -2 h. Continued declines in photoperiod for post-teneral locusts (transitioned from -1h until fledging to -1.75 h) produced a further increase in the proportion of diapause eggs. The results were unaffected by time spent at any given photoperiod, despite a previously indicated maximal inductive photoperiod of 13.5h being used as the mid-point of all treatments. Implications for the seasonal timing processes of photoperiodism in C. terminifera, which has a high migratory capacity and a latitudinal cline in the timing of diapause egg production across a broad geographic range, are discussed.

The Adelaide Philosophical Society and the early accommodatin of the Darwin-Wallace Theory of Natural Selection

Abstract Evolution was a topic much discussed in Adelaide before and after the arrival of the theory of natural selection, particularly its consequences for the relationship between science and theology. The Adelaide Philosophical Society (1853–1880) was a focus for readings of developments in evolutionary theory and these were widely reported in the South Australian press. Through newspaper accounts of two of its members’ activities, this paper documents the interpretation of evolution and Darwinian theory in colonial Adelaide. Charles Algernon Wilson provided early views of the natural history of the colony in the South Australian press from 1840. Wilson’s writings reflect changing views of nature and, through his connection with Alfred Russel Wallace, contributed to scientific explanation of Natural Selection. Richard Davies Hanson introduced the developmental theory in 1849 and followed with a series of lectures during 1860–1864 that dealt with the social and religious implications of science and theories of evolution.

The Australian Plague Locust—Risk and Response

Abstract Locust plagues are natural hazards that have been historically regarded as disasters because of their impact on agricultural production. In Australia during the nineteenth and early twentieth centuries, the impacts of locusts led to significant hardships among farmers struggling to establish viable individual livelihoods. The use of pesticides for locust control and the establishment during the 1970s of coordinated response arrangements has significantly mitigated the economic and social impact of plagues. The main risk now is of control failure, which could lead to major economic losses, but significant concern also exists about unnecessary interventions; contamination of nontarget crops, pastures, and livestock; effects on natural ecosystems; and injuries and health hazards for control staff and the general public. Establishment of a national specific-purpose locust control organization with expert staff and formal links to regional stakeholders has allowed development of appropriate and effective responses to these risks. These responses have now been formalized as defined operating procedures. Mitigating the risks of locust control is ultimately as important as mitigating the impact of the locust plagues themselves.

Locusts in Southern Settler Societies: Argentine and Australian Experience and Responses, 1880–1940

Locust invasions were a problem common to many colonial settler societies, for whom agricultural development was crucial to success. Their impact on crops and pastures caused repeated losses and hardships for the nascent farming enterprises. In the southern lands of Argentina and Australia the initial hopes that bringing more land under cultivation, restoring the ‘balance of nature’, using disease organisms for biological control, or collective labour would solve the problem faded as swarms kept appearing. An increase in the frequency and intensity of plagues during the late nineteenth century created a fear that farming might become impossible and an urgency to find scientific solutions. The migrations of swarms across provincial boundaries and areas of cultivation propagated the risk of damage over wide geographic regions and into subsequent seasons. This led to government involvement in organising and funding collective responses and directing scientific research into locust ecology.