ECOLOGY OF HOST ALTERNATION IN APHIDS

This paper reviews the evidence for the fundatrix specialization hypothesis and attempts to quantify the relative advantage of host alternation and define the conditions favouring the evolution of this way of life. Contrary to the predictions of the fundatrix specialization hypothesis there does not appear to be a barrier to some host alternating Aphidinae transferring their whole life cycle over to a secondary host plant. The coexistence of plants with asynchronous phenologies supplied the potential and the ability of aphids to produce a number of highly prolific generations in quick succession, which amplify the differences in performance on the two hosts and more than offsets the costs of transfer between hosts, supplies the means of exploiting this potential. That is, host alternation is not maladaptive and maintained by constraint but adaptive, at least in the Aphidinae.