Temporal variation in herbivore host-plant preference and performance: constraints on host-plant adaptation

Temporal variation in the acceptability or suitability of plant genotypes to an herbivore has seldom been considered as a possible constraint limiting the adaptation of herbivores to particular plant genotypes, or the occurrence of a positive correlation between host-plant preference and offspring performance. In this study, we used data spanning 12 yr from the same 20 clones of goldenrod (Solidago altissima) to examine the temporal variation in oviposition preference and offspring performance of a stem-galling fly, Eurosta solidaginis. We found that the stem galler's preference for, or performance on, the different clones was uncorrelated between years of this study. Furthermore, we found that the relative rankings of clones changed by an average of 31% between successive years. We suggest that these consistently high year-to-year fluctuations in preference and performance by E. solidaginis are likely due to environmental factors (e.g., water and nutrient levels, or abundance of interspecific herbivores) that fluctuate over time and are known to differentially affect the acceptability and suitability of clones to herbivores; i.e., genotype x environment interactions. These results are significant because temporal fluctuations in host-plant preference and performance are likely to favor a more generalized diet by herbivorous insects.