Host genotype choice by the ball gallmaker Eurosta solidaginis (Diptera: Tephritidae)

We examined Eurosta solidaginis host choice among 38 naturally occurring clones of tall goldenrod, Solidago altissima. Significant variation was found in the percentages of (1) ramets ovipunctured, (2) punctured ramets with eggs, (3) ramets galled, and (4) punctured ramets that formed galls. These findings indicate that all genotypes of S. altissima are not equally suitable (capable of supporting larval development and/or acceptable (having the proper cues to stimulate oviposition). The two most resistant and two of the most susceptible of 38 clones were monitored for ovipuncturing the following season. A total of 244 apical buds on ramets were dissected at intervals of 1, 2, and 3 wk after oviposition. Significantly more larval mortality occurred in the meristems of resistant clones than in the meristems of susceptible clones. Further, 73% of the dead Eurosta larvae were surrounded by necrotic plant tissue, apparently due to a hypersensitive response by the plant to the gallmaker's stimulus. Finally, a common garden experiment using replicates of 30 clones of known resistance showed that susceptible clones were growing faster at the time of oviposition.