Impact of Prolonged Absence of Low Temperature on Adult Eclosion Patterns of Western Cherry Fruit Fly (Diptera: Tephritidae).

Western cherry fruit fly, Rhagoletis indifferens (Curran) (Diptera: Tephritidae), is a serious pest of cherries (Prunus spp.) in the Pacific Northwest of the United States. Previous research suggests that R. indifferens is unlikely to establish in commercial cherry production areas in California and in tropical export markets because cold temperatures, below 5 °C, in those regions appear insufficient to complete diapause. However, it is unclear how prolonged absence of cold exposure affects diapause termination in R. indifferens. Here, we examined this question by exposing R. indifferens pupae for 40 wk to simulated temperate and tropical conditions of 23 or 26 °C, 40 or 80% RH, and a photoperiod of 16:8 or 12:12 (L:D) h. Eclosion patterns among fly groups in the four conditions did not differ. For all groups, fly eclosion from pupae not exposed to cold exhibited a bimodal distribution. The first major peak, comprising 3.2% of the total fly emergence, occurred at 1-10 wk. The second major peak, comprising the remaining 96.8%, occurred at a mode of ∼30 wk. Based on responses to no cold and cold (3 ± 1.5 °C) exposures, there were three distinct pupal diapause groups: the first eclosion group was likely nondiapausing pupae; the second eclosion group was likely diapausing pupae; a third group that remained viable but did not produce adults after 40 wk may represent prolonged dormancy pupae. We suggest that eclosion of adults after prolonged absence of cold exposure needs to be incorporated into models for potential fly establishment in warm climates.