Assessing the risk of establishment of western cherry fruit fly (Diptera: Tephritidae) in commercial cherry-growing areas of California

Ecological niche modeling was used to assess the risk of establishment of western cherry fruit fly, Rhagoletis indifferens Curran (Diptera: Tephritidae), in sweet cherry, Prunus avium (L.) L., in the commercial cherry-growing areas of California.  We integrated species occurrence records and spatial environmental variables using three ecological niche modeling algorithms (Maxent, logistic regression, and boosted regression trees) to assess the potential risk of establishment of R. indifferens.  All models performed better than random and resulted in highly significant correlations between observed presence-(pseudo) absence and predicted probability of presence.  An ensemble model predicted a very low risk for R. indifferens establishment in the San Joaquin Valley around the areas where sweet cherries are produced.  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 in association with its native host, bitter cherry [Prunus emarginata (Douglas) Eaton].  Human footprint index (human-associated plantings of sweet cherry and irrigation), bitter cherry distribution, minimum temperature of coldest month, and direct solar radiation (a surrogate for photoperiod) were the top predictors of R. indifferens distribution.  Overall results suggest that R. indifferens is unlikely to establish in the commercial cherry-growing areas in the San Joaquin Valley of California, largely because chilling requirements in those areas are not met.