Use of a geographic information system to explore spatial variation in pathogen virulence and the implications for biological control of locusts and grasshoppers

1 In a previous study, we developed a model to predict the effects of temperature on performance of a fungus-based biopesticide for controlling locusts and grasshoppers. Currently, the model is limited to predicting rate of mortality after a spray application at site-specific locations. The aim of the present study is to enhance the utility of this model by linking it with meteorological station data in a geographic information system (GIS) framework to investigate the spatial variation in the performance of the biopesticide. 2 The model provides maps that define spatial variation in pathogen virulence (measured as LT₉₀ for a treated population) across different regions. The model was used to explore the variation in biopesticide performance against four economically important pest species: Moroccan locust Dociostaurus maroccanus in Spain; brown locust Locustana pardalina in South Africa; red locust Nomadacris septemfasciata in Zambia and; Senegalese grasshopper Oedaleus senegalensis in Niger. 3 Model outputs for the different species were partially validated against data from field trials. The models provided good estimates of time to 90% mortality for five out of six independent comparisons. There was also good agreement between the spatial model and equivalent output from the site-specific model. 4 Simulations of virulence against N. septemfasciata in Zambia indicated very uniform, rapid mortality with LT₉₀ throughout the country generally less than 11 days. Pathogen-induced mortality of O. senegalensis in Niger was predicted to be slightly slower and more variable with mortality fastest in the southern regions (< 15 days) and slowing to the north of the country (16-20 days). For both L. pardalina in South Africa and D. maroccanus in Spain, the model revealed highly variable patterns of mortality with LT₉₀ ranging from < 15 days in some areas to > 30 days in others. 5 The implications of these different patterns of variability for the development of optimum use strategies for the various species and the basic understanding of the ecology and evolution of insect-pathogen interactions are discussed.