Energetics of the Solidago Canadensis‐stem Gall Insect‐parasitoid Guild Interaction

Energy budgets are developed for two goldenrod stem gall insects: Eurosta solidaginis (Diptera: Tephritidae) and Gnorimoshema gallaesolidaginis (Lepidoptera: Gelechiidae). Energy budgets are also constructed for the parasitoid guilds associated with each of the gall insects. Over 25 kJ or °7% of mean ramet production were used in formation of these falls and support of the insects. If the gall insects were parasitized, only 15—20 kJ were used in gall and insect production. The ecological efficiencies of energy transfer between the gall insects and their parasites on a square—metre basis were 10 and 8% for Eurosta and Gnorimoshema, respectively. These insect energetics are then related to Harnett and Abrahamson's (1979) results for the effects of the two stem gall insects on resource allocation patterns in goldenrod, where gall—bearing ramets compared to non—gall—bearing ramets showed decreases of 45% (Eurosta) and 28% (Gnorimoshema) in ramet porgagule production. The energy lost form the ramet by having a ball gall is greater than is accounted for by energy flow into the gall, and the presence of either gall can have an appreciable impact on plant fitness.