Response of the aphid specialist Uroleucon nigrotuberculatum to clones of Solidago altissima growing at different elevations

There is considerable interest in factors responsible for the selection of host plants by herbivorous insects, especially when an insect strongly prefers certain plant species. Aphids represent a common and significant herbivore of many old-field community plant species and their choice of plants could be shaped by both genetic differences (i.e. clones) between conspecifics and where individual plants grow in the environment. We used experiments employing a common garden approach to ask if the aphid Uroleucon nigrotuberculatum, a specialist of plants in Asteraceae, colonized the clonally reproducing tall goldenrod, Solidago altissima, based on patches where ramets were collected (small spatial scale) and the elevation plants grew (large spatial scale). Ramets collected from Eastern Tennessee at 260, 585, 885 and 1126m were propagated from 3cm rhizomes and planted in a natural old-field setting. Aphids varied in abundance mostly based on differences between clones, though within elevation effects of clone were evident. Insect colonization was most affected by the environment in which plants grew at the lowest elevation. Important plant nutritional constituents for herbivores (N and CN) were related more to clone than elevation. However, within clones collected at the highest elevation (1126 m), there were no significant effects for N and CN, suggesting that the environment plants grew in played a stronger role. For some defensive terpenoid compounds elevation had a greater effect than clone, once again suggesting a role for environment rather than small-scale genetic differences. Our data provides evidence that a specialist herbivore colonizes its preferred host plant due to intraspecific genetic variation and that the environment in which clonal plant species grow can affect insect choice.