Jr. Layne et Re. Medwith, WINTER CONDITIONING OF 3RD INSTARS OF THE GALL FLY EUROSTA-SOLIDAGINIS (DIPTERA, TEPHRITIDAE) FROM WESTERN PENNSYLVANIA, Environmental entomology, 26(6), 1997, pp. 1378-1384
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.