Evaluating correlative and mechanistic niche models for assessing the risk of pest establishment

Insect pests pose a great threat to global food security. Improved methods for assessment of the risk of pest establishment are needed to enhance informed decision-making, to develop cost-effective pest management strategies, and to design quarantine policies for preventing the spread of pests. We evaluated the capabilities of a correlative and a process-based mechanistic niche model, and their combination, to assess the risk of pest establishment. The correlative model MaxEnt and the process-based mechanistic model CLIMEX were used to assess the risk of establishment of western cherry fruit fly, Rhagoletis indifferens Curran (Diptera: Tephritidae) in California. We integrated R. indifferens occurrence records and spatial environmental variables using MaxEnt to assess the potential risk of establishment of this pest. The CLIMEX model was developed using eco-physiological tolerances of R. indifferens. The predictive performance of the MaxEnt model improved by including the host species' distribution and Ecoclimatic Index generated using the CLIMEX model. The best model predicted no risk for R. indifferens establishment in the Central Valley around the areas where sweet cherries are produced in California. Most of the high to very high risk areas for R. indifferens were predicted in northern parts of California and the Sierra Nevada Mountains, where the fly exists on its native host, bitter cherry [Prunus emarginata (Douglas) Eaton]. Precipitation of driest quarter, degree days with average temperatures >= 8.3 degrees C, degree days with average temperatures <= 58 degrees C, and mean diurnal range in temperature were the strongest predictors of R. indifferens distribution in western North America. We showed that the predictive power of correlative niche models can be improved by including outputs from the process-based mechanistic niche models. Overall results suggest that R. indifferens is unlikely to establish in the commercial cherry-growing areas in the Central Valley of California, largely because heat stress is too high and chilling requirement in those areas is not met.