Conserved cold tolerance of Rhagoletis species from different host fruits, elevations in Colorado, USA
Understanding and characterizing how insects tolerate low temperatures is important for predicting their overwintering survival and subsequent geographic spread. This study characterized the cold tolerance of two members of the Rhagoletis genus in Colorado, U.S.A. Pupae were collected from infested fruit in late summer and early fall. For the first time, we show that the rosehip fly Rhagoletis basiola is freeze-avoidant; overwintering pupae could supercool to temperatures as low as -26{degrees}C and survive. Interestingly, the temperature at which ice forms (supercooling point; SCP) did not vary between R. basiola at high (c. 2900 m above sea level) and lower (c. 1650 m a.s.l.) elevations. We also report the apple maggot Rhagoletis pomonella infesting an unusual host fruit, the Dolgo crabapple, in close proximity to infested hawthorn trees. R. pomonella infesting hawthorn fruits and crabapples had similar SCPs, and survived temperatures as low as -21{degrees}C. Pupae from both host fruits also survived prolonged exposure (2 weeks or more) to mild low temperatures (0 to -5{degrees}C). Further study into the mechanisms underlying the impressive and conserved cold tolerance of R. pomonella and R. basiola is an interesting avenue for future research.