Host interaction and regulation in parasitoid wasps

Author: Jennifer Pan

Introduction

Successful parasitism by insect parasitoids is a complex evolutionary process. The parasitoid insect must locate a host, overcome the host immune response, and adapt to a constantly changing environment to satisfy the metabolic and nutritional needs of the immature parasitoid. Parasitic organisms have diverse origins and have evolved a variety of developmental strategies to exploit their host (Brodeur and Boivin, 2004). While several orders of insects include parasitoids, the Hymenoptera are a particularly diverse order of holometabolous insects that are abundant in terrestrial areas throughout the world (Whitfield, 1998). Parasitoid wasps belong to the Hymenoptera order and are important for biological control since they reduce pest populations by parasitizing various species of insects. Not only are they ecologically important, parasitoid wasps greatly contribute to insect diversity. Recent estimates indicate that around 10% to 20% of all insects are parasitoid wasps (Quicke, 1997). Just as they demonstrate extensive species diversity, parasitoid wasps display a wide variety of interactions with their hosts.

Wasps commonly parasitize other insects by attacking a particular host life stage, such as the eggs, larvae, pupae, or adults. Parasitoids are classified into two groups: idiobionts and koinobionts . The difference between these two types is that a host ceases to develop after being infested by an idiobiont, whereas a host will continue to develop after being infested by a koinobiont (Askew and Shaw, 1986). Iodobionts are either ectoparasitoids that develop outside the host or endoparasitoids that develop inside the host. Koinobionts are usually endoparasitoids of larval stage insects, and only a few are ectoparasitic. Both ectoparasitoids and endoparasitoids have developed a variety of strategies to escape or overcome their host’s immunity defenses and regulate the host’s physiology to allow for their own development (Beckage and Gelman, 2004).