ECOLOGY OF HOST ALTERNATION IN APHIDS

This paper reviews the evidence for the fundatrix specialization hypot hesis and attempts to quantify the relative advantage of host alternat ion and define the conditions favouring the evolution of this way of l ife. Contrary to the predictions of the fundatrix specialization hypot hesis there does not appear to be a barrier to some host alternating A phidinae transferring their whole life cycle over to a secondary host plant. The coexistence of plants with asynchronous phenologies supplie d the potential and the ability of aphids to produce a number of highl y prolific generations in quick succession, which amplify the differen ces in performance on the two hosts and more than offsets the costs of transfer between hosts, supplies the means of exploiting this potenti al. That is, host alternation is not maladaptive and maintained by con straint but adaptive, at least in the Aphidinae.