A fundamental objective in biology is to understand the evolutionary and ecological
processes that lead to patterns of diversity. Specialized insect-host relationships have long
been suspected of facilitating evolutionary diversification due to the intimate relationship
parasites share with their hosts and the potential for disruptive selection when utilizing
different host species resulting in genetic divergence. However, the vast majority of
research investigating insect-host specialization has focused on herbivores, while the
mechanisms of population and species divergence in insects that parasitize and kill other
insects (parasitoids) have been largely ignored. Parasitoids have great potential for
research in host-specialization and speciation due to their unique biological properties
and the immens\; diversity that is ,characteristic of this ecologically important guild. '.
The goal of my Ph.D. thesis was to contribute to the greater understanding of host
specialization and speciation in parasitoid wasps, with a particular focus on the processes
that drive adaptive diversification and the behavioural mechanisms that maintain genetic
variation. These topics were addressed through a combination of experimental biology,
fieldwork and theoretical modelling using a host-parasite system consisting of a single
parasitoid (Aphidius ervi) and two host species (the pea aphid, Acyrthosiphon pisum and
the foxglove aphid, Aulacorthum solani).
Specifically, the physiological mechanism involved in overcoming host defences was
investigated to determine if parasitoids adaptively evolve to overcome host defences and
ifthis process is under directional selection. Host fidelity, host plant preference, mating
preference, and host-instar selection were investigated to determine the importance of
these behaviours in mediating gene flow between parasitoid populations utilizing
different host species. In combination, these studies further contribute to our basic
understanding ofthe mechanisms that lead to and maintain genetic diversity in insect
parasitoids.
