Parasitoid Wasps and Their Venoms

Parasitoid wasps are a unique group among venomous organisms. In contrast to the common venom functions of predation and defense, female parasitoid wasps use venom to manipulate the metabolism, development, and behavior of other arthropods for reproductive purposes. This provides a safe environment and nutrition for the next generation of wasps to feed and develop. Parasitoid wasp species diversity is estimated to be between 150,000 and 600,000 species, likely making them the largest group of venomous organisms. They parasitize all orders of Insecta and several taxa from Arachnida. Parasitoids display highly diverse morphologies and parasitic lifestyles. This diversity likely plays a strong role in the adaptive evolution of venom apparatus structures, venom genes, and venom functions. However, parasitoid wasps are underexplored and little represented in toxinology. This chapter provides a background into evolution of parasitoid wasps and their parasitic lifestyle. The evolution of parasitoid venoms and their functions are discussed, and a comparison of venom functions in two major ecological categories, ectoparasitoids and endoparasitoids, is provided. Expanding on the standard gene duplication and recruitment model of toxin gene evolution, additional mechanisms are proposed. These include co-option, multifunctionalization, alternate splicing, and origins from lateral gene transfers or noncoding DNA. Novel tools such as RNA interference (RNAi) knockdown of parasitoid venom genes, combined with RNA sequencing of envenomated hosts, are proposed for venom function hypothesis testing and hypothesis generation. This chapter also addresses key questions concerning the future directions of parasitoid venom research.