WINTER CONDITIONING OF 3RD INSTARS OF THE GALL FLY EUROSTA-SOLIDAGINIS (DIPTERA, TEPHRITIDAE) FROM WESTERN PENNSYLVANIA

Third instars of Eurosta solidaginis (Fitch) inhabit stem galls on gol denrod, Solidago spp., exposing them to cold, desiccation, and tempera ture instability. Because these conditions increase the risk of metabo lic stress, the physiological conditioning of 3rd instars was examined between September and March for 2 successive years (1993-1994 and 199 4-1995). The maximum and minimum air temperatures differed by 63 and 5 0 degrees C during 1993-1994 and 1994-1995, respectively. Subnormal te mperatures prevailed most of the winter for 1993-1994, whereas an oppo site trend existed during 1994-1995. Although subfreezing temperatures were still common during both years, temperatures were often above th e larval supercooling point. The water content of larvae was stable th roughout the study but their body mass and lipid content declined near ly 20% during each study period. Hemolymph osmolality rose from 0.5 Os moles (September) to just above 1.3 Osmoles (January). The supercoolin g point rose from -11.4 to -9.8 degrees C between September and Octobe r; it then remained stable until declining in March. Some changes seen here (e.g., reducing supercooling capacity) likely facilitate the win ter survival of the larvae; whereas, other physiological changes (e.g. , loss of stored lipids) represent passive responses to the harsh gall environment, Moderate differences in winter severity between the 2 yr failed to appreciably alter larval use of energy reserves or their ma intenance of cryoprotectant levels.