Ducking as a means of resistance to herbivory in tall goldenrod, Solidago altissima.

Many populations of goldenrod show a peculiar, genetically controlled stem dimorphism. In Solidago altissima, for instance, while most stems are erect, a sizable minority (the "candy-cane" stems) nod at the apex during growth. We used data from three studies to test the hypothesis that this candy-cane growth form confers resistance to herbivory. In a controlled growth trial, we showed that nodding is a temporary phenomenon that coincides with the oviposition period of at least two common apex-attacking herbivores: the tephritid galler Eurosta solidaginis and the gall midge Rhopalomyia solidaginis. In a large field survey, stems of candy-cane genets were only half as likely to be ovipunctured by E. solidaginis. In a common-garden study, candy-cane stems were less likely to be ovipunctured by E. solidaginis, and they were galled only half as often by R. solidaginis as erect stems. These results suggest that the candy-cane stems of goldenrod possess a resistance strategy that allows them to essentially duck and hide from certain herbivores.