Divergent responses of two cereal aphids to previous infestation of their host plant

We examined the effects of prior infestation by the Russian wheat aphid [Diuraphis noxia (Mordvilko)] and the bird cherry-oat aphid [Rhopalosiphum padi (L.)] on the subsequent feeding preferences and performance of each species. Aphid colonies fed and reproduced on wheat seedlings for five days and were then removed. After a period of plant recovery, we estimated aphid population growth and feeding preferences on control and previously infested plants. Previous infestation by D. noxia had no effect on the subsequent population growth of either aphid species. Previous infestation by R. padi reduced its own subsequent growth by 50%, but had little effect on the population growth of D. noxia. When presented leaves from control plants and D. noxia-infested plants, D. noxia adults preferred to feed on leaves from control plants; R. padi adults showed no preference. Both aphids preferred leaves from control plants to those from R. padi-infested plants. In free-flight cages, alates of R. padi settled more often and produced more progeny on control plants than on plants previously infested by R. padi, but their rates of settling and reproduction were unaffected by prior D. noxia infestation. Together, our results suggest specificity in both the plant response to the two aphid species (plant quality for R. padi was lowered by prior R. padi infestation but not by D. noxia infestation) and in each aphid's response to the same modification of the host plant (infestation by R. padi reduced plant quality for itself but not for D. noxia). Effects of prior infestation on the feeding preferences of R. padi were correlated with effects on performance.