Indirect population interaction between two aphid species

We designed an experiment to test whether two species of aphid feeding on different species of host plant influence each others population dynamics via shared parasitoids (apparent competition) or other indirect processes. Pea aphid (Acyrthosiphon pisum) colonies declined faster towards mid-summer when there were nearby colonies of nettle aphid (Microlophium carnosum), though the significance of the difference (P = 0.06) was just short of the traditional 0.05 level. Observations suggested that parasitoids were not responsible for this difference, however, and that it was highly likely to be caused by aphid-specific predators.