Assessing the potential for establishment of western cherry fruit fly (Rhagoletis indifferens) using MaxEnt and CLIMEX niche models

Sweet cherries, Prunus avium (L.) L., grown in the western United States are exported to many countries around the world. Some of these countries have strict quarantine rules and trade restrictions due to concerns about the potential establishment and subsequent spread of western cherry fruit fly, Rhagoletis indifferens Curran (Diptera: Tephritidae), a major quarantine pest of sweet cherry. We evaluated (i) niche models (MaxEnt and CLIMEX) to map the climatic suitability, (ii) NAPPFAST to examine chilling requirement, and (iii) host distribution and availability to assess the potential for establishment of R. indifferens in areas of western North America where it currently does not exist and in eight current or potential fresh sweet cherry markets: Colombia, India, Indonesia, Malaysia, Taiwan, Thailand, Venezuela, and Vietnam. Results from niche models conformed well to the current distribution of R. indifferens in western North America. MaxEnt and CLIMEX models had high performance and predicted climatic suitability in some of the countries (e.g., Andean range in Colombia and Venezuela, northern and northeastern India, central Taiwan, and parts of Vietnam). However, our results showed no potential for establishment of R. indifferens in Colombia, Indonesia, Malaysia, Taiwan, Thailand, Venezuela and Vietnam when the optimal chilling requirement to break diapause (minimum temperature ≤3°C for at least 15 weeks) was used as the criterion for whether establishment can occur. Furthermore, these countries have no host plant species available for R. indifferens. Our results can be used to make scientifically informed international trade decisions and negotiations by policy makers.