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HYMENOPTERA, Braconidae (Kirby 1837) - (Ichneumonoidea).

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Description & Statistics

Braconidae. -- All species of the braconids are parasitic on other insects. They sting the host and thereby paralyze it.

There are more than 1850 North American species most of which are beneficial. The adults are all fairly small rarely exceeding 16 mm in long. Many are stout-bodied than the ichneumons, and the abdomen is about as long as the head and the thorax combined. They are similar to ichneumonids by lacking a costal cell, but they differ by not having more than one recurrent vein. Many species are valued as natural controls of pest insects.

Braconids and ichneumonids have similar habits, but unlike the ichneumonids many pupate in silken cocoons on the outside of the body of their hosts, while others spin silken cocoons entirely apart from the host. Polyembryony occurs in a few species, primarily in the genus Macrocentrus, each egg of M. grandis Goidanich, a parasitoid of the European corn borer, develops into from 16 to 24 larvae.

This 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.

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 species 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 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."

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. 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.

Natural History

The family dates 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 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.

The species Microplitis croceipes possesses an extremely accurate sense of smell and can be trained for use in narcotics and explosives detection.

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References: Please refer to <biology.ref.htm>, [Additional references may be found at: MELVYL Library]

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