Conserved cold tolerance ofRhagoletisspecies from different host fruits, elevations in Colorado, USA

Abstract

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 theRhagoletisgenus 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 flyRhagoletis basiolais freeze-avoidant; overwintering pupae could supercool to temperatures as low as −26°C and survive. Interestingly, the temperature at which ice forms (supercooling point; SCP) did not vary betweenR. basiolaat high (c. 2900 m above sea level) and lower (c. 1650 m a.s.l.) elevations. We also report the apple maggotRhagoletis pomonellainfesting an unusual host fruit, the Dolgo crabapple, in close proximity to infested hawthorn trees.R. pomonellainfesting hawthorn fruits and crabapples had similar SCPs, and survived temperatures as low as −21°C. Pupae from both host fruits also survived prolonged exposure (2 weeks or more) to mild low temperatures (0 to −5°C). Further study into the mechanisms underlying the impressive and conserved cold tolerance ofR. pomonellaandR. basiolais an interesting avenue for future research.