The Braconidae constitute one of the most species-rich families of insects. Although tropical faunas are still relatively poorly understood at the species level, most taxonomists in this group would agree that a rough, probably highly conservative, estimate of 40-50,000 species worldwide is reasonable as an extrapolation from the current described number of roughly 12,000 species. Among extant groups, the sister group of the Braconidae is the Ichneumonidae, an equally enormous group (Sharkey and Wahl, 1992; Quicke et al. 1999).
The family appears to date from early Cretaceous (assuming Eobracon is properly assigned to family - Rasnitsyn, 1983; Whitfield, 2002), diversifying extensively in the mid to late Cretaceous and early Tertiary, when flowering plants and their associated holometabolous herbivores, the main hosts for braconid parasitoids, radiated (Basibuyuk et al., 1999; Quicke et al., 1999; Belshaw et al., 2000; Whitfield, 2002). The species richness of the family is matched by a morphological diversity virtually unrivalled among the Hymenoptera. They range in size from approximately 1 mm in length to 3-4 cm (not counting the ovipositor, which in some species can be several times as long as the body).
Figure 1. Microgastrine braconid adult female (length approx. 2 mm). Image copyright © 2004 James B. Whitfield
Some of the groups are parts of extensive Müllerian mimicry complexes (Quicke, 1986), and exhibit striking color patterns (some of which are recurrent within regions), while others are among the most inconspicuous of Hymenoptera. The braconids display a bewildering array of wing venation patterns and body forms to stymie the beginning student. Female external genitalia (ovipositor mechanisms) vary considerably intraspecifically and are widely used for species discrimination;
Figure 2. Ovipositior mechanism of Andesipolis, for reaching into plant tissue. Image copyright © 2004 Won-Young Choi
Figure 3. Ovipositor mechanism of Cotesia, for inserting eggs into exposed caterpillars. Image copyright © 2004 Won-Young Choi
while the male genital capsules tend to be somewhat more conservative and have been underutilized relative to other insect groups.
Figure 5. Male genital capsule of Hypomicrogaster, from a relatively derived (microgastroid) lineage.
Image copyright © 2004 Josephine Rodriguez
These tiny to small wasps have black legs, antennae, and wings, otherwise they are variously colored; they are more stout than Ichneumonid wasps. Braconids are parasitoid on various small insects. They obtain nectar from wildflowers, particularly members of the Carrot family, but are easily overlooked. They do not construct special brood nests, but fly off after implanting an egg on a host insect.
Chrysididae (Cuckoo Wasps)
These wasps are are metallic green or blue, with an integument that is thick, hard, and sometimes coarsely pitted. Cuckoo wasps have ovipositors, but usually lack stingers. They are usually brood parasites on other wasps and bees, but some species are parasitoid on walking sticks, sawfly larvae, and other insects. Cuckoo wasps are occasional visitors to flowers; they are not particularly common.
There are three different groups of Braconidae that attack fruit-infesting Tephritidae. The most frequently encountered braconids are members of the subfamily Opiinae. They are koinobiont endoparasitoids ovipositing in the host egg or larval stage and emerging as adult wasps from the host puparium. Additional details are provided under Diachasma , Diachasmimorpha , Doryctobracon , Fopius , Opius , Psyttalia , Sternaulopius , and Utetes.
The second group belongs to the subfamily Alysiinae. They are closely related to the Opiinae (Opiinae and Alysiinae are sister groups within the Braconidae) and have similar biologies. Most of the alysiines reared from fruits attack flies other than members of the family Tephritidae, but there are a few species routinely reared from fruit-infesting tephritids. Additional details are provided under Asobara and Microcrasis.
The third group belongs to the subfamily Braconinae. Several species of Bracon have been reared from fruit-infesting Tephritidae, and additional details are provided in a separate page for Bracon. Nearly all of the Braconinae reared from fruit (and all of the ones attacking Tephritidae) are idiobiont ectoparasitoids of the larval stages of their hosts.
Several other groups of Braconidae are commonly reared from insect-infested fruit, but these attack either lepidopteran or coleopteran larvae. Among these are members of the subfamilies Agathidinae, Cheloninae, and Microgastrinae (all parasitoids of lepidopteran larvae) and the Helconinae (parasitoids of coleopteran larvae). There are some records of Helconinae (Nealiolus sp. and Triaspis) from fruit-infesting tephritids, but I regard these as doubtful and in need of confirmation. The species that Silvestri (1914) recorded as Sigalphus daci from olives in Transvaal, for example, is a member of the genus Triaspis. All other species of Triaspis are parasitoids of Coleoptera. For example, Triaspis eugenii has been reared from the pepper weevil, Anthonomus eugenii, in Mexico and has been studied for use as a biological control agent in Florida (Wharton and López-Martínez 2000).
Keys to the world subfamilies and general introductions to the literature are available in van Achterberg (1993) and Sharkey (1993). A new manual to the genera of the New World has been produced (Wharton et al., 1997 - Spanish version 1998), including individual subfamily chapters contributed by a number of the world's braconid specialists. Interactive versions of the keys in this manual are available online. van Achterberg (1997) has published the CD-ROM
The higher classification of the Braconidae has been a matter of much dispute. Approximately 40 subfamilies are generally recognized, several of them newly discovered within the last 15 years (Mason, 1983; Quicke, 1987; Whitfield and Mason, 1994). Several subfamilies (e.g., Aphidiinae, Alysiinae, Apozyginae) have at one time or another been recognized as separate families. In general there is agreement on the basic subfamily or tribal groupings, with the exception of the "hormiine" and "exothecine" groups of genera (Whitfield, 1992; Quicke, 1993; Wharton, 1993b), but disagreement on the ranking or inclusiveness of some groups, since our understanding of the phylogeny of the family is not yet robust. There is a general perception that the number of recognized subfamilies has become inflated, while the tribal rank has been underutilized. An attempt has been made to address this problem (Wharton, 2001), but requires further phylogenetic testing.
The vast majority of braconids are primary parasitoids of other insects, especially upon the larval stages of Coleoptera, Diptera, and Lepidoptera but also including some hemimetabolus insects (aphids, Heteroptera, Embiidina). As parasitoids they almost invariably kill their hosts, although a few only cause their hosts to become sterile and less active. Both external and internal parasitoids are common in the family, and the latter forms often display elaborate physiological adaptations for enhancement of larval survival within host insects, including the co-option of endosymbiotic viruses for compromising host immune defenses (Stoltz and Vinson, 1979; Stoltz, 1986; Whitfield, 1990; Beckage, 1993, Stoltz and Whitfield, 1992; Whitfield, 2002; Whitfield and Asgari, 2003).
Early larval development in braconids has also yielded surprises, such as the discovery of relatively closely related genera that differ in such import aspects as syncitial versus holoblastic cleavage, normally characterizing major animal phyla (Grbic and Strand, 1998; Grbic, 2000)! Parasitism of adult insects (especially of Hemiptera and Coleoptera) is also known, and members of two subfamilies (Mesostoinae and Doryctinae) form galls on plants (Infante et al., 1995; Austin and Dangerfield, 1998). Several excellent general reviews of braconid biology are available (Matthews, 1974; Shaw and Huddleston, 1991; Shaw, 1995; Wharton, 1993a).
Figure 6. Microplitis ceratomiae larvae emerging from sphingid caterpillar.
Image copyright © 2004 James B. Whitfield
Figure 7. Sphingid caterpillar with cocoons of Cotesia congregata.
Image copyright © 2004 Sydney A. Cameron
Evolution and Systematics
Discussion of Phylogenetic Relationships
Early attempts to explore the phylogeny of the major groups of Braconidae (e. g., Tobias, 1967; van Achterberg, 1984) were largely intuitive. Quicke and van Achterberg (1990) made the first large-scale effort to estimate braconid phylogeny using a large data set of morphological characters, and computer-assisted parsimony analysis. Although many aspects of this study have been in dispute (Wharton et al., 1992; van Achterberg and Quicke, 1992), it has stimulated a number of further attempts at resolving the phylogeny of subset groups of the Braconidae, using morphology as well as molecular data (e. g. Belshaw and Quicke, 1997; Whitfield, 1997; Belshaw et al., 1998; Dangerfield et al., 1999; Dowton et al., 1998; Dowton, 1999; Mardulyn and Whitfield, 1999; Quicke and Belshaw, 1999; Quicke et al., 1999; Belshaw et al., 2000; Kambhampati et al., 2000; Sanchis et al., 2000; Belshaw et al., 2001; Dowton et al., 2002; Whitfield et al., 2002; Chen et al. 2003).
The phylogeny used as the backbone here for accessing the subfamilies is adapted and pasted together, with a great deal of conservative poetic license, from these recent studies. It should not be taken all that seriously, as help is on the way in the form of continuing morphological and molecular phylogenetic studies. The reader is encouraged to consult the literature cited above for more in-depth analysis.
Molecular Biology and Genetics
Statistics of barcoding coverage
|Specimen Records:||52,139||Public Records:||27,990|
|Specimens with Sequences:||43,400||Public Species:||2,918|
|Specimens with Barcodes:||36,841||Public BINs:||4,619|
|Species With Barcodes:||3,357|
Locations of barcode samples
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.
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 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. 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.
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.
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.
- ^ Piper, Ross (2007), Extraordinary Animals: An Encyclopedia of Curious and Unusual Animals, Greenwood Press.
- ^ Drezen, Jean-Michel; Lanzrein, Beatrice; Volkoff, Anne-Nathalie; Huguet, Elisabeth; Dupuy, Catherine; Periquet, Georges; Pfister-Wilhem, Rita; Belghazi, Maya; Heller, Manfred; Roditi, Isabel; Wincker, Patrick; Bernard-Samain, Sylvie; Gyapay, Gabor; Wetterwald, Christoph; Herbinière, Juline; Annaheim, Marc; Bézier, Annie (February 13, 2009). "Polydnaviruses of Braconid Wasps Derive from an Ancestral Nudivirus". Science (Science Magazine) 323 (5916): 926–930. doi:10.1126/science.1166788. PMID 19213916. http://www.sciencemag.org/cgi/content/abstract/323/5916/926. Retrieved 2009-02-13.
- ^ Wharton, Robert M. (2000), "Can braconid classification be restructured to facilitate portrayal of relationships?", in Austin, Andrew D.; Dowton, Mark, Hymenoptera: evolution, biodiversity, and biological control, 4th International Hymenopterists Conference, Collingwood, Victoria, Australia: Commonwealth Scientific and Industrial Research Organisation (CSIRO), pp. 143–153, ISBN 0 643 06610 1
- ^ The Scoop: Move Over, Rover. November 20, 2001