All About Braconid Wasps of the Family Braconidae

Braconid wasp cocoons on a hornworm.
Braconid wasp cocoons on a hornworm. Photo: © Debbie Hadley, WILD Jersey

Experienced gardeners love braconid wasps, the beneficial parasitoids that so visibly and effectively kill their despised tomato hornworms. Braconid wasps (family Braconidae) perform an important service by keeping pest insects under control.  

Description

Braconid wasps are an enormous group of rather tiny wasps that vary greatly in form, so don't expect to identify them accurately without the help of an expert.

They rarely reach more than 15mm in length as adults. Some braconid wasps are inconspicuously marked, while others are brightly colored. Certain braconids even belong to Müllerian mimicry rings.

Braconid wasps look similar to their close cousins, the ichneumonid wasps. Members of both families lack costal cells. They differ in having just one recurrent vein (2m-cu*), if present at all, and fused second and third tergites.

Classification:

Kingdom – Animalia
Phylum – Arthropoda
Class – Insecta
Order – Hymenoptera
Family - Braconidae

Diet:

Most braconid wasps drink nectar as adults, and many show a preference for nectaring on flowers in the mustard and carrot plant families.

As larvae, braconids consume their host organism. Certain subfamilies of braconid wasps specialize on particular groups of host insects. Some examples include:

  • Aphidiinae – parasitoids of aphids
  • Neoneurinae – parasitoids of worker ants
  • Microgastrinae – parasitoids of caterpillars
  • Opiinae – parasitoids of flies
  • Ichneutinae – parasitoids of sawflies and leaf-mining caterpillars

Life Cycle:

Like all members of the order Hymenoptera, braconid wasps undergo complete metamorphosis with four life stages: egg, larva, pupa, and adult. The adult female usually oviposits into or on the host organism, and the braconid wasp larva emerges ready to feed on the host.

In some braconid species, like those that attack hornworm caterpillars, the larvae spin their cocoons in a group on the body of the host insect.

Special Adaptations and Defenses:

Braconid wasps carry the genes of polydnaviruses within their bodies. The virus replicates within the braconid wasp eggs as they develop within the mother. The virus doesn't harm the wasp, but when the egg is deposited into a host insect, the polydnavirus is activated. The virus prevents the host organism's blood cells from recognizing the parasitoid egg as a foreign intruder, enabling the braconid egg to hatch.

Range and Distribution:

The braconid wasp family is one of the largest insect families, and  includes over 40,000 species worldwide. They are widely distributed throughout the world, wherever their host organisms are present.

* See Insect Wing Venation Diagram for more information on the recurrent vein.

Sources:

  • Bugs Rule: An Introduction to the World of Insects, by Whitney Cranshaw and Richard Redak.
  • Borror and DeLong's Introduction to the Study of Insects, 7th Edition, by Charles A. Triplehorn and Norman F. Johnson.
  • Encyclopedia of Entomology, 2nd Edition, edited by John L. Capinera.
  • Family Braconidae – Braconid Wasps, Bugguide.net. Accessed online April 4, 2014.