Researchers have recently focused on effects of genetic diversity on a wide range of ecological processes. In particular, several studies have addressed effects of plant genetic diversity on higher trophic levels. However, it is poorly understood how population structure of herbivores is influenced by plant genetic diversity. To examine effects of mixtures of tall goldenrod Solidago altissima genotypes on population structure of the aphid Uroleucon nigrotuberculatum, we conducted field experiments in the common garden in Minnesota, USA.

In monoculture experiment of genets, we found resistant and susceptible genotypes against the aphids. Plant height partially contributed to resistance/susceptibility. Next, in monoculture vs mixture experiments, aphid density significantly increased in the mixture of plant genotypes, but not in the monoculture. Even in the mixture, aphid density did not change on susceptible genotypes but increased on resistant genotypes. This is because aphids colonized to resistant patches (sink) from susceptible ones (source), indicating the metapopulation structure within closely spaced plants. This study suggests that plant genotypic diversity would have non-additive effect on herbivore abundance through maintaining metapopulation structure of herbivore population.