Previous infestation affects recolonization of cotton byAphis gossypii: induced resistance or plant damage?

Abstract

The effect of previous infestation by the cotton aphid (Aphis gossypii Glover) on resistance of cotton seedlings to further infestation by the same insect, was examined in the laboratory. Seedlings which survived a heavy infestation and produced new leaves, were recolonized artificially and the fate of the colonizers was monitored. The two cotton varieties used in the experiments differed in resistance to aphid colonization, and a few seedlings were initially unsuitable for aphid colonization. Aphids transferred to new leaves on previously infested plants were not so successful as on uninfested seedlings and repeated attempts over a few weeks were sometimes required until a colony became established. Reinfested plants often showed no visible signs of stress, but the aphid colonies were frequently of the ‘yellow dwarf’ morph, indicating that the plants had been stressed after the first infestation. We suggest that damage caused by the first infestation — and not the production of some excess metabolites — is the reason for the lower success on previously infested plants.