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Parasitoid wasps exhibit a wide range of interactions with hosts. In order to successfully parasitize their hosts, wasps must overcome their host’s immune response and a number of ecological constraints. Consequently, parasitoid wasps have evolved a variety of developmental strategies to effectively exploit their host. The evolution of parasitoid diversity in wasps can be explained by tracing the evolutionary history of these organisms and understanding the ecological factors that affect parasitoid development. Developmental strategies differ among species of parasitoid wasps with respect to these evolutionary and ecological factors. Parasitoid wasps use various physiological and molecular tools to escape their host’s immune response. While some species use passive mechanisms to avoid recognition, other species produce factors that suppress or destroy the host’s immunity. Venoms from female parasitoid wasps are injected into the host to disrupt host development, while symbiotic polydnaviruses (PDVs) are used to infect host tissues and similarly suppress the host’s immune system. Analysis of the different mechanisms of wasp parasitism provides valuable insight to the evolution of biological diversity in this group of insects.

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).

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Source:  OpenStax, Mockingbird tales: readings in animal behavior. OpenStax CNX. Jan 12, 2011 Download for free at http://cnx.org/content/col11211/1.5
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