The larvae of most braconids are internal or external
primary parasitoids of other
insects, especially the
larval stages of
Coleoptera,
Diptera, and
Lepidoptera, but also some
hemimetabolous insects such as
aphids,
Heteroptera, or
Embiidina. Most species kill their hosts, though some cause the hosts to become
sterile and less active. Parasitoidy on adult insects (particularly on Hemiptera and Coleoptera) also occurs. Members of two subfamilies, the
Mesostoinae and
Doryctinae are known to form
galls on plants. Braconids are often used as
biological pest control agents, especially against aphids.
Examples of hosts Thousands of species of insects are used as hosts by braconid wasps. A few notable examples are detailed here. Some species of braconids are parasitoids of
Ostrinia furnacalis (the Asian corn borer, a lepidopteran moth known for being a pest of
maize in East Asia), the
African sugarcane borer (a moth commonly found in sub-Saharan Africa), the butterfly
Danaus chrysippus in
Ghana, and
Liriomyza trifolii (the American serpentine leafminer) and
Manduca quinquemaculata (the tomato hornworm) in North America. Braconids often will prey on fruit fly larvae like
Anastrepha suspensa as well.
Polydnaviruses Endoparasitoid species often display elaborate physiological adaptations to enhance larval survival within the host, such as the co-option of
endosymbiotic viruses for compromising host
immune defenses. These
bracoviruses are often used by the wasps instead of, or in addition to, a venom cocktail. The DNA of the wasp actually contains portions that are the templates for the components of the viral particles and they are assembled in an organ in the female's abdomen known as the calyx. A 2009 study has traced the origins of these templates to a 100-million-year-old viral infection whose alterations to its host DNA provided the necessary basis for these virus-like "templates". These viruses suppress the immune system and allow the parasitoid to grow inside the host undetected. The exact function and evolutionary history of these viruses are unknown. Sequences of polydnavirus genes show the possibility that venom-like proteins are expressed inside the host caterpillar. Through the evolutionary history of being used by the wasps, these viruses apparently have become so modified, they appear unlike any other known viruses today. Because of this highly modified system of host
immunosuppression, a high level of parasitoid-host specificity is not surprising. ==Evolutionary history==