The impacts of climate change on the overwintering energetics and microenvironmental conditions of the goldenrod gall fly, Eurosta solidaginis

Larvae of the goldenrod gall fly (Eurosta solidaginis) have long served as model organisms for studying the strategies used by freeze-tolerant animals for winter survival. The larvae of this insect undergo a marked transition from freeze intolerant to freeze tolerant during fall and, at our field site in Pennsylvania, enter diapause during mid- to late-October.  These larvae then remain dormant throughout winter relying on accumulated lipids and glycogen as metabolic substrates.  The winter temperatures experienced by the larvae directly influence the potential fecundity of the adults, as the energy reserves remaining at the end of winter determine body size and are used for gamete production in the flies.  Therefore, the purpose of the present study was to assess the current and future impacts of climate change on the overwintering energetics and microenvironmental conditions experienced by E. solidaginis larvae.  We used historical temperature data to estimate the overwintering (November through March) energy used by larval gall flies.  Based upon the relationship between metabolic rate and temperature, the estimated energy utilization during winter has increased by nearly 30% over the last 50 years.  Each additional 1^oC rise in temperature is predicted to increase overwintering energy consumption by ~13%.  Continued climate change will also have significant impacts on the winter thermal microenvironment of E. solidaginis.  Elevated winter temperatures are predicted to significantly decrease the number of freeze-thaw cycles, the average time spent frozen per cycle, the total time spent frozen during winter, and the minimum winter temperature experienced by the larvae.