Habitat Selection and Colony Survival of Macrosiphum valeriani Clarke (Homoptera: Aphididae)

Abstract

In screenhouse cage experiments, apterous Macrosiphum valeriani Clarke walked onto potted fireweed (Epilobium (=Chaemerion) angustifolium (L.)) shoots nearest release points without regard to the presence or densities of other M. valeriani or of Aphis varians Patch, an aphid competitor. Alate M. valeriani chose tall fireweed, but without regard to A. varians. In field experiments, however, M. valeriani placed on fireweed shoots with A. varians had significantly lower survival and reproduction than those placed on shoots with no aphids. These surprising results can be reconciled proximately because other insects (including predators) were excluded from the cage experiments, and ultimately because competition between these aphids is not likely in nature because of short colony survival of both species due to predation. For these aphids, habitat selection and performance are not closely linked to competition between the aphids, as assumed and predicted by models of habitat selection.