INTERSPECIFIC COMPETITION BETWEEN ROOT-FEEDING AND LEAF-GALLING APHIDS MEDIATED BY HOST-PLANT RESISTANCE

Host-mediated interactions were explored for two aphid species that feed on Chenopodium. Pemphigus betae feeds underground on roots, while Hayhurstia atriplicis feeds aboveground where it forms leaf galls. Although they never encounter one another directly, these 2 aphid species shared a common resource, the phloem sap of their host. The root-feeding aphid P. betae had no significant effects on its hosts, but leaf galling by H. atriplicis reduced overall host mass by an average of 54% and seed set by 60%. Competitive interactions between the herbivore species depended on the level of host resistance to leaf galling by H. atriplicis. On susceptible plants, leaf-galling colonies of H. atriplicis reduced P. betae numbers by an average of 91%, often eliminating the root feeders entirely. On plants resistant to galling, H. atriplicis colonies were smaller and did not affect P. betae infesting roots of the same hosts. Although H. atriplicis had a strong negative effect on P. betae, the latter showed no measurable effects on H. atriplicis. Resistance to leaf-galling aphids is not correlated with resistance to root-feeding aphids in this system. -from Authors