Parasites, politics and public science: the promotion of biological control in Western Australia, 1900-1910.

Biological control of arthropods emerged as a scientific enterprise in the late nineteenth century and the orchard industry of California was an early centre of expertise. In 1900, as the Australian colonies prepared for federation, each had a government entomologist attached to its agriculture department. The hiring of George Compere from California by the Western Australian Department of Agriculture began a controversial chapter in the early history of biological control that was linked to a late, local popularization of acclimatization. Compere became known as the 'travelling entomologist' and for a decade brought 'parasites' of pest insects from overseas and released them in Perth. His antagonistic disciplinary rhetoric and inflated claims for the 'parasite theory' created conflict with his counterparts in the eastern states. The resulting inter-state entomological controversy was played out in the press, revealing the political use of science for institutional and even state identity. It is a story of transnational exchanges, chance discoveries and popular public science: popular because of the promise of a simple, natural solution to agricultural insect pests and because of the public nature of the disputes it generated between the experts. This microcosm contributes to the global historiography of acclimatization, biological control, scientific exposition and the professionalization of agricultural science.

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.

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.

Daily mapping of Australian Plague Locust abundance.

Locust population outbreaks have been a longstanding problem for Australian agriculture. Since its inception in the mid-1970s, The Australian Plague Locust Commission (APLC) is responsible for monitoring, forecasting and controlling populations of several locust pest species across inland eastern Australia (ca. two million km2). Ground surveys are typically targeted according to prevailing environmental conditions. However, due to the sheer size of the region and limited resources, such surveys remain sparse. Here we develop daily time-step statistical models of populations of Chortoicetes terminifera (Australian plague locust) that can used to predict abundances when observations are lacking, plus uncertainties. We firstly identified key environmental covariates of locust abundance, then examined their relationship with C. terminifera populations by interpreting the responses of Generalized Additive Models (GAM). We also illustrate how estimates of C. terminifera abundance plus uncertainties can be visualized across the region. Our results support earlier studies, specifically, populations peak in grasslands with high productivity, and decline rapidly under very hot and dry conditions. We also identified new relationships, specifically, a strong positive effect of vapour pressure and sunlight, and a negative effect of soil sand content on C. terminifera abundance. Our modelling tool may assist future APLC management and surveillance effort.

Future climate change likely to reduce the Australian plague locust (Chortoicetes terminifera) seasonal outbreaks.

Climate is a major limiting factor for insect distributions and it is expected that a changing climate will likely alter spatial patterns of pest outbreaks. The Australian plague locust (APL) Chortoicetes terminifera, is the most economically important locust species in Australia. Invasions cause large scale economic damage to agricultural crops and pastures. Understanding the regional-scale and long-term dynamics is a prerequisite to develop effective control and preventive management strategies. In this study, we used a 32-year locust survey database to uncover the relationship between historical bioclimatic variables and spatial seasonal outbreaks by developing two machine learning species distribution models (SDMs), random forest and boosted regression trees. The explanatory variables were ranked by contribution to the generated models. The bio-climate models were then projected into a future climate change scenario (RCP8.5) using downscaled 34 global climate models (GCMs) to assess how climate change may alter APL seasonal distribution patterns in eastern Australia. Our results show that the model for the distribution of spring outbreaks performed better than those for summer and autumn, based on statistical evaluation criteria. The spatial models of seasonal outbreaks indicate that the areas subject to APL outbreaks were likely to decrease in all seasons. Multi-GCM ensemble means show the largest decrease in area was for spring outbreaks, reduced by 93-94% by 2071-2090, while the area of summer outbreaks decreased by 78-90%, and 67-74% for autumn outbreaks. The bioclimatic variables could explain 78-98% outbreak areas change. This study represents an important step toward the assessment of the effects of the changing climate on locust outbreaks and can help inform future priorities for regional mitigation efforts in the context of global climate change in eastern Australia.

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.