Ecology and radiation of galling aphids (Tamalia; Hemiptera: Aphididae) on their host plants (Ericaceae)

At least two species of aphid, Tamalia coweni and Tamalia dicksoni (Hemiptera: Aphididae) induce galls on the leaves of Arctostaphylos spp. shrubs (Ericaceae). These galls are frequently inhabited by at least one species of congeneric inquiline. The inquiline clade has branched off from the gall-inducing clade and appears to be radiating rapidly on different host-plants, in contrast to the gall inducers. This striking pattern may offer insight into the factors driving speciation. Three key innovations present ecological opportunities for Tamalia gall-inducers and inquilines: (1) the induction of galls not only on leaf margins, but also on leaf midribs and inflorescences, both of which are novel host plant organs for Tamalia. (2) Gall-induction on wellarmed host plants, otherwise protected with dense and viscous pubescence. (3) The origin of the inquiline habit in congeneric Tamalia aphids is a shift into a novel adaptive zone. Inquiline Tamalia exploit gall-inducers by competing successfully within the gall. They may have specialized along host-plant lines because of the critical need for precise timing with the plant during the gall invasion process. & 2005 Gesellschaft für Ökologie. Published by Elsevier Gmbh. All rights reserved.