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

Abstract

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 LT 90 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 LT 90 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 LT 90 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.

Development of a model for evaluating the effects of environmental temperature and thermal behaviour on biological control of locusts and grasshoppers using pathogens

“…It has a role in interpreting patterns of mortality after application, providing locust control officers with real-time guidance as to when to expect substantial levels of mortality, and for prospective analysis to identify candidate targets for biocontrol and optimize use strategies. We are currently working to increase the utility of this model by linking with meteorological station data in a Geographic Information Systems framework to enable area-wide applications ( Klass et al , 2007 ).…”

Rethinking vector immunology: the role of environmental temperature in shaping resistance

“…More fundamentally, although numerous modelling studies (including some excellent recent work informing contemporary control strategies 89,90 ) integrate aspects of the effects of environmental temperature, none includes the possible effects of temperature on vector resistance, which could be responsible for much of the variation in vector competence over time and space. Modelling work quantifying the spatial and temporal variation in the susceptibility of locusts and grasshoppers to fungal insect pathogens used in biological control provides an interesting illustration of the practical value of understanding temperature-dependent resistance and virulence 91,92 .…”

Thermoregulatory behaviour affects prevalence of chytrid fungal infection in a wild population of Panamanian golden frogs

“…This is especially true for ectotherms where ambient conditions constrain the physiological temperatures of both host and pathogen (Carruthers et al 1992;Blanford & Thomas 1999Jackson & Tinsley 2002;Blanford et al 2003;Klass et al 2007;Laine 2008;Lazarro et al 2008). Several experimental studies have now demonstrated an effect of temperature on the susceptibility and behaviour of ectotherm hosts and/or the virulence of their pathogens (e.g.…”

“…However, the functional mechanisms underlying these effects and their potential to affect the outcomes of infections under natural conditions are not well understood (Carey et al 1999;Jackson & Tinsley 2002). A clearer understanding of the links between environmental factors and the outcomes of host-pathogen interactions will probably provide valuable insights into host-pathogen coevolution and epidemiology, as well as more fundamental aspects of the ecology and evolution of interspecific interactions (Lambrechts et al 2006;Klass et al 2007). Given the potential impact of ongoing climate change on disease risk for humans (McMichael 2006;Estrada-Pena 2009) and other organisms (e.g.…”