| Braconidae | |
|---|---|
| A member of the braconid genus Atanycolus. | |
| Scientific classification | |
| Kingdom: | Animalia |
| Phylum: | Arthropoda |
| Class: | Insecta |
| Order: | Hymenoptera |
| Superfamily: | Ichneumonoidea |
| Family: | Braconidae |
| Subfamilies | |
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Braconidae is a family of parasitoid wasps and one of the richest families of insects. Between 50,000 and 150,000 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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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 Müllerian mimicry complexes. They have one or no recurrent veins, unlike other members of the Ichneumonoidea which usually have two. Wing venation patterns are also divergent to apparent randomness. 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. Species that parasitize microlepidoptera, for instance, have longer ovipositors, presumably to reach the caterpillar through layers of plant tissue. Some wasps also have long ovipositors because of caterpillar defense mechanisms such as spines or hairs.
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. 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 polydnaviruses are often used by the wasps instead of 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.[1] 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".[2]
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.
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 parasitoids that attack host eggs or larvae; hence they are often utilized as biological pest control agents, especially against aphids.
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.
Braconidae is traditionally divided into more than 40 subfamilies. These fall to two major groups, informally called the cyclostomes and non-cyclostomes. In cyclostome braconids, the labrum and the lower part of the clypeus are concave with respect to the upper clypeus and the dorsal margin of the mandibles. These groups may be clades that diverged early in the evolution of braconids.[3]
Braconidae is distiguished from its sister group Ichneumonidae by the following character combinations. In Braconidae, vein 2m-cu of the forewing is absent- this vein is present in 95% of Ichneumonidae. Vein 1/Rs+M of the forewing is 85% present in Braconidae but absent in all Ichneumonidae. Vein 1r-m of the hind wing is in 95% of Braconidae basal to the separation of R1 and Rs (it is opposite or apical in Ichneumonidae). In Braconidae Metasomal tergum 2 is fused with tergum 3, (secondarily flexible in Aphidiinae) - 90% of Ichneumonidae have a flexible suture.[4]
The species Microplitis croceipes possesses an extremely accurate sense of smell and can be trained for use in narcotics and explosives detection.[5]
Braconidae are very resistant to ionizing radiation. While dose of only 4.5 Gy is sufficient to kill an average human.[6] Braconidae can survive an exposure roughly 400x greater requiring ~1800 Gy.[7]
On the University of Florida / Institute of Food and Agricultural Sciences Featured Creatures website: