Cotesia congregata

Cotesia congregata
Scientific classification
Kingdom:	Animalia
Phylum:	Arthropoda
Class:	Insecta
Subclass:	Pterygota
Order:	Hymenoptera
Superfamily:	Ichneumonoidea
Family:	Braconidae
Subfamily:	Microgastrinae
Genus:	Cotesia
Species:	Cotesia congregata

Cotesia congregata is a parasitic wasp of the genus Cotesia.

Life cycle

Adult wasps lay their eggs in tobacco hornworm larvae (2nd or 3rd instar [each instar is between moltings, i.e. the second instar is the life stage after the first molt and before the second molting) and at the same time injects symbiotic viruses into the hemocoel of the host. The viruses knock down the internal defensive responses of the hornworm (Buron and Beckage, 1992; Beckage, 1997). The eggs hatch in the host hemocoel within two to three days and simultaneously release special cells from the egg chorion (Buron and Beckage, 1997). These special cells, called teratocytes, grow to become giant cells visible to the naked eye. The function of teratocytes is not yet known but several roles have been hypothesized, such as inhibiting pupation or being involved in the depression of the host’s defensive system (see in Buron and Beckage, 1997). Following hatching in the caterpillar, the wasp larvae will undergo 2 molts inside the host caterpillar’s hemocoel and, after 12 to 16 days post oviposition, the 3rd instar wasp larvae will emerge out of the caterpillar and spin cocoons from which the adult wasps fly about 4 to 8 days later. ---From: [1]

C. congregata manipulates its host hemolymph ecdysteroid levels by interfering with the normal inhibitory mechanisms that prevent PTG (prothoracic gland) production and release of ecdysteroid at inappropriate periods of insect growth and development. However, the mechanism by which this action occurs is unknown. Perhaps, parasitoid-produced proteins are involved, because parasitoids have been observed to release proteins under both in vivo and in vitro conditions.

The PDVs of larval-larval parasitoids are known to interfere with host's development. The symptoms of this phenomenon include either the induction or suppression of metamorphic changes in the host, both of which are due to endocrine disruption. Particularly in Manduca sexta larvae that are infected by C. congregata, the endocrine effects become obvious in the host's last instar, when metamorphic symptoms are suppressed regardless of the size of the host caterpillar. The host's weight may exceed 5 g (the weight that normally triggers the onset of metamorphosis). Thus, any further life stage development in the host is arrested as a larva. It then lives for several days in a nonfeeding state before death occurs two to three weeks following egression of the wasps from the host. Nonparasitized fourth-instar M. sexta caterpillars that are injected with C. congregata PDV attain abnormally high weights (up to 18 g) as fifth instars and then die as premetamorphic larvae or larval-pupal intermediates, which suggests that their hemolymph JH levels remain high enough to suppress metamorphosis. In this system, venom is not required to induce endocrine disruption of the host.

References

• arjournals.annualreviews.org