Braconidae
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Braconidae is a family of parasitoid wasps and one of the richest family of insects. From the approximate 12,000 described species (the braconids), it is extrapolated that between 40,000 and 50,000 species exist worldwide. The species are grouped into about 45 subfamilies and 1,000 genera, some important ones being: Ademon, Aphanta, Asobara, Bracon hebetor, Cenocoelius, Chaenusa, Chorebidea, Chorebidella, Chorebus, Cotesia, Dacnusa, Microgaster, Opius, Parapanteles , Phaenocarpa, Psenobolus.
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[edit] Morphology
The morphological variation among braconids is notable. Braconids are often black-brown (sometimes with reddish markings), though some species exhibit striking coloration and pattern, being parts of the Müllerian mimicry complexes. They have one or no recurrent veins, contrarily to other members of the Ichneumonoidea which usually have two. Wing venation patterns are also very various. The antennae have 16 segments or more; the hind trochanters have 2 segments.
Females often have long ovipositors, an organ that largely varies intraspecifically. This variation is closely related to the host species upon which the wasp deposits its egg. For instance species that parasitize microlepidoptera have longer ovipositers; presumably to reach the caterpillar through layers of plant tissue. Some wasps also have long ovipositers because of caterpillar defense mechanisms such as spines or hairs.
[edit] Parasitism
Most braconids are primary parasitoids (both external and internal) on other insects, especially upon the larval stages of Coleoptera, Diptera, and Lepidoptera, but also some hemimetabolous insects like aphids, Heteroptera or Embiidina. Most species kill their hosts, though some cause the hosts to become sterile and less active. In the case of endoparasitoids, species often display elaborate physiological adaptations to enhance larval survival within host, for example the co-option of endosymbiotic viruses for compromising host immune defenses. These polydnaviruses are often used by the wasps instead of a venom cocktail. 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. It is a little surprising to consider that sequences of polydnavirus genes show the possibility that venom-like proteins are expressed inside the host caterpillar. It appears that through evolutionary history the wasps have so highly modified these viruses that they appear unlike any other known viruses today. Because of this highly modified system of host immunosuppression it is not surprising that there is a high level of parasitoid-host specificity. It is this specificity that makes Braconids a very powerful and important biological control agent.
Parasitism on adult insects (particularly on Hemiptera and Coleoptera) is also observed. Members of two subfamilies (Mesostoinae and Doryctinae) are known to form galls on plants.
[edit] Larval development
Surprisingly, both syncitial and holoblastic cleavage are present, even in closely related taxa.
Larvae can be found on hosts as diverse as aphids, bark beetles, and foliage-feeding caterpillars. Many species are egg-larval parasitoids; hence they are often utilized as biological pest control agents, especially against aphids.
[edit] Natural history
The family seems to date from early Cretaceous (provided that Eobracon is properly assigned to this family). It underwent extensive diversification from mid or late Cretaceous to early Tertiary, correlating with the radiation of flowering plants and associated herbivores, the main hosts of braconids.
[edit] Trivia
The species Microplitis croceipes possesses an extremely accurate sense of smell and can been trained for use in narcotics and explosives detection[1]
