Potential global crop pest distributions using CLIMEX: HarvestChoice Applications

Executive Summary: HarvestChoice provides data, information and tools to support strategic investment decisions in agriculture. Most agricultural processes are strongly influenced by biotic stressors, such as insects and pathogens. However, available pest information has been lacking, for example global maps of where pests and diseases could occur have not been available. To address this deficiency, HarvestChoice has developed and implemented an approach to pest modeling aimed directly at supporting strategic decisions in agriculture. The HarvestChoice system includes methods, techniques and tools to both collect primary data on pest occurrence and to model potential global pest occurrence. In addition, a global team of recognized pest and climate experts has been assembled to aid in modeling, validation and peer-review. The pest modeling system developed by HarvestChoice differs from the more typical monitoring and prediction systems that support short- to medium-term objectives, such as responding to pest events. Rather, we support strategic decision-making by mapping not where pests occur, but where they might potentially occur. This approach allows us to answer hypothetical questions that were previously unanswerable. For example, we can provide broad information on what portion of the world’s crop area could be subject to a pest or what might happen if a new variety were planted in a previously un-cropped location. The end results of our efforts are maps of potential pest occurrence. These maps are produced by modeling a species’ response to factors such as temperature and moisture, while carefully keeping certain other factors exogenous (namely, those factors that might be decision variables for strategic planning). For example, the models are not conditional on the actual presence of a susceptible host, so our maps show the potential pest distribution assuming that susceptible hosts occur everywhere, avoiding confounding the host climate responses with those of the pest. The models combine geo-spatial climate data and information on the seasonal phenology of each pest to investigate potential growth, stress and persistence of pests on a global scale. Growth is measured by a “Growth Index,” higher values of which indicate a higher potential for that the pest’s population to grow at a given location. Potential growth is restricted by sub-optimal temperatures or moisture and the pest’s survival is limited by stresses, such as extremely cold or dry conditions. A final index, the “Ecoclimatic Index,” is calculated by considering the extent to which growth is possible during the favorable season and survival is limited by the stresses during the non-growth season at each location. The result of this calculation, the Ecoclimatic Index is a measure of the potential ability of the pest to persist and develop high population sizes at a location: that is, whether it can survive the extremes of summer, winter, dry and wet seasons. This Working Paper describes the HarvestChoice approach to pest modeling and places that work in the context of other pest mapping efforts.