Differential Cold Tolerance on Immature Stages of Geographically Divergent Ceratitis capitata Populations

SIMPLE SUMMARY: Ceratitis capitata, also known as the Mediterranean fruit fly, is a notorious pest of fruits and vegetables worldwide. The current expansion of its geographic distribution is limited by the cooler temperate areas of the Northern Hemisphere, which points to a more comprehensive investigation of its thermal biology considering its high invasion capacity. Cold tolerance in adults has been studied thoroughly but the impact of extremely low temperatures on the immature stages remains unexplored. We estimated the acute cold stress response of three geographically divergent populations (two from Greece and one from Croatia). Overall, the populations exhibited different responses to acute cold stress depending on the developmental stage. The northernmost population was the most cold-susceptible at the egg stage, whereas in the southernmost population it was at the larval and pupal stage. The geographically intermediate population was the most cold-tolerant regardless of the developmental stage. The egg stage was the most cold-tolerant, followed by pupae and larvae. Our findings broaden the existing knowledge on cold tolerance of C. capitata and can be used for the development of population and invasion dynamics models. ABSTRACT: Cold tolerance of adult medflies has been extensively studied but the effect of subfreezing temperatures on the immature stages remains poorly investigated, especially as far as different populations are regarded. In this study, we estimated the acute cold stress response of three geographically divergent Mediterranean fruit fly populations originating from Greece (Crete, Volos) and Croatia (Dubrovnik) by exposing immature stages (eggs, larvae, pupae) to subfreezing temperatures. We first determined the LT(50) for each immature stage following one hour of exposure to different temperatures. Then eggs, larvae and pupae of the different populations were exposed to their respective LT(50) for one hour (LT(50) = −11 °C, LT(50) = −4.4 °C, LT(50) = −5 °C for eggs, larvae and pupae, respectively). Our results demonstrate that populations responded differently depending on their developmental stage. The population of Dubrovnik was the most cold-susceptible at the egg stage, whereas in that of Crete it was at the larval and pupal stage. The population of Volos was the most cold-tolerant at all developmental stages. The egg stage was the most cold-tolerant, followed by pupae and finally the 3rd instar wandering larvae. This study contributes towards understanding the cold stress response of this serious pest and provides data for important parameters that determine its successful establishment to unfavorable environments with an emphasis on range expansion to the northern, more temperate regions of Europe.