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Braconidae is one of the largest families of parasitic wasps in the Hymenoptera and is estimated to include at least 40,000 species, although only about a 15,000 of these species have been described. The Braconidae family has been divided into about 35 subfamilies, and the subfamilies of greatest interest are: Agathidinae, Alysiinae, Blacinae, Braconinae, Doryctinae, Euphorinae, Homolobinae, Microgastrinae, and Opiinae (Quick 1997). Wasps belonging to the Braconidae family exclusively parasitize other insects and are therefore greatly beneficial for pest control. Braconids are found throughout the world, but most species prefer warm, dry climates. As a result, braconids have been extensively used in biological control programs in tropical and subtropic areas (Gauld and Bolton 1988).
The braconid wasp Toxoneuron nigriceps is an endoparasitoid of the tobacco budworm that uses polydnaviruses, to control its host’s development. After T. nigriceps injects venom containing polydnavirus into its host, teratocytes produce a chitinase just before the parasitoid larva emerge from the host. The chitinase is involved in facilitating the emergence of parasitoid larva by digesting the host cuticle since parasitoid larva lack mandibular apparatus (Consoli et al 2005).
In addition to polydnaviruses in the female ovary, several different types of virus-like particles (VLPs) have been discovered in the accessory glands of various braconid species. In a recent study by Luo and Zeng (Luo and Zeng 2010) a new rod-shaped virus was found in the accessory gland filaments of the parasitoid wasp D. longicaudata. This braconid parasitizes several species of fly pests and has been used to control fly populations in Thailand.
In order to successfully parasitize the host, parasitoid wasps must generate and release gene products at oviposition that alter the physiology of the host (Vinson and Iwantsh, 1980). One of the most important morphological adaptations in Hymenoptera that arose to accommodate parasitoid lifestyle was the venom gland (Quicke, 1997). All female hymenopterans internally store poisonous venom in their ovaries and secretory organs. The venom gland appears to produce factors that are injected into hosts or prey that can also be injected into intruders as defensive secretions. Ectoparasitic idiobionts inject venom into hosts that is often paralytic and causes developmental arrest of the host, which benefits the externally developing parasite (Doury et al., 1995). Parasitoid wasps produce a wide range of venoms that could serve as models for developing synthetic chemical insecticides.
One species that has been extensively studied for its venom is the fly ectoparasitoid Nasonia vitripennis . This parasitoid wasp feeds and lays eggs on large flesh fly pupae. Adult females of this species inject venom prior to oviposition and the envenomated fly eventually dies from venom toxicity (Danneels et al 2010).
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