Genotypic interactions in an aphid-host plant relationship: Uroleucon rudbeckiae and Rudbeckia laciniata.

Four clones of the aphid Uroleucon rudbeckiae were grown on four clones of the host plant Rudbeckia laciniata. Age-specific fecundities were used to determine the fitness, F' i , of each individual aphid. The analysis of variance for F' i revealed that (1) plant genotype has a significant effect on aphid fitness; (2) there is an interaction between aphid and host plant genotypes with respect to aphid fitness; and (3) aphid fitness is affected by phenotypic differences among individual host plants. Result (2) supports the hypothesis that genotypic interactions between aphid and host may maintain genetic diversity in aphid populations. The results of a preference test, while not significant at customary probability levels, suggested that aphids will choose to feed on plants which confer greater fitness.