Clumped distribution patterns in goldenrod aphids: genetic and ecological mechanisms

1. The aphids Uroleucon tissoti and U. nigrotuberculatum both exhibit significantly aggregated distribution patterns across clumps of their common host plant Solidago altissima, the tall goldenrod. However, U. nigrotuberculatum is significantly more aggregated than is U.tissoti. We tested the hypothesis that goldenrod genotype-by-U. tissoti genotype interactions for aphid performance characters could partially account for this difference. 2. Only one of the characters we measured showed a significant genotype-bygenotype interaction; therefore it is unlikely that such interactions affect the distribution of U. tissoti across goldenrod stems. 3. In addition, we found that three environmental variables (genetic variation for resistance to herbivory, host plant morphology, and local host density) affect the degree of aggregation found in both U.tissoti and U.nigrotuberculatum populations.