WINTER MICROCLIMATE OF GOLDENROD SPHERICAL GALLS AND ITS EFFECTS ON THE GALL INHABITANT EUROSTA-SOLIDAGINIS (DIPTERA, TEPHRITIDAE)

1. The microclimate of spherical galls on goldenrod (Solidago) was monitored and the condition of goldenrod gallfly (Eurosta solidaginis) larvae also assessed during winter in western New York, U.S.A. 2. Gall temperature was highly labile and changed more than 20-degrees-C on some days. While galls closely followed air temperature at night, they often warmed several degree-C above air temperature on sunny days. Gall water content was even more labile, failing as low as 10% and rising above 60% of the total mass during the observation period. 3. Larvae showed little change in their body mass and hemolymph osmolality changed moderately. Evidence of natural freezes was obtained but these did not last more than 2-3 days at a time. Natural hydration of galls caused larvae to move from the central gall cavity into the exit tunnel and restored the capacity of gall tissues to cause inoculative freezing. 4. In summary, galls are highly labile environments that are greatly affected by the prevailing weather, however, Eurosta larvae seem adept at coping with these conditions.