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 mon itored and the condition of goldenrod gallfly (Eurosta solidaginis) la rvae also assessed during winter in western New York, U.S.A. 2. Gall t emperature was highly labile and changed more than 20-degrees-C on som e days. While galls closely followed air temperature at night, they of ten warmed several degree-C above air temperature on sunny days. Gall water content was even more labile, failing as low as 10% and rising a bove 60% of the total mass during the observation period. 3. Larvae sh owed little change in their body mass and hemolymph osmolality changed moderately. Evidence of natural freezes was obtained but these did no t 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 af fected by the prevailing weather, however, Eurosta larvae seem adept a t coping with these conditions.