IRWIN, Jason T*; WHIPPLE, Amy P; HEINRICH, Paul L; ABRAHAMSON, Warren G; Bucknell University: Exploring winter energy consumption as a limitation to the southern range limit of the goldenrod gall fly (Eurosta solidaginis) on late goldenrod (Solidago gigantea)

The goldenrod gall fly, Eurosta solidaginis, is a gall-forming insect that has formed two host races on two species of goldenrod: Solidago gigantea and S. altissima. These two host races show appreciable reproductive isolation and genetic differentiation. Flies of the altissima host race can be found virtually everywhere its host plant is found (from northern Florida northward into Canada). Although S. gigantea is as widely distributed as S. altissima, gall flies of the gigantea host race are only found on its host in the northern tier of the range of S. gigantea (from Maine to Iowa). The gigantea host race is both smaller in mass and less fecund than the altissima host race. We performed a series of experiments to identify the factors restricting the gigantea host race to northern locales. Our data show that the southern limit of gigantea flies is most closely correlated with warm winter temperatures. The small size of gigantea flies is related to the earlier senescence (and thus cessation of feeding) in S. gigantea than S. altissima, and possibly to host-plant food quality. Being smaller, the gigantea host race has less energy support metabolism during winter and egg production the following spring (adults do not feed). We will present our ongoing efforts to produce a model of winter energy use of goldenrod gall flies across their range, and subsequent spring fecundity. Our work will stand as an important model for predicting shifts in geographic distribution of insects with global climate warming.