parasitoid larvae pupating on a caterpillar

Insect parasitoids have a very specialised life cycle that includes an immature stage that develops on or within a single insect host, ultimately killing that host. The life cycle begins when an adult female insect parasitoid lays her eggs on or in the body of a host insect, such as a caterpillar. The parasitoid larvae, after hatching, feed on the body tissues of the host insect, eventually killing it. Once the larvae have fully developed, the larvae will either pupate inside the host or form a cocoon outside.

The life cycle and reproductive habits of parasitoids can vary greatly between species. For example, in some species, only one parasitoid will develop in or on each host while, in other species, hundreds of larvae may develop within the host. Insect parasitoid life cycles may also vary in which life stage of their host they attack - some parasitoids will lay their eggs near the eggs of their host, while other species will lay their eggs in or on the larvae of their host. Usually insect parasitoids will only attack a particular life stage of one or several related species. The most common insect parasitoids are wasps and flies.

The photo above shows a tobacco hornworm (Manduca sexta) that has been parasitised by a species of braconid wasp. The larvae of the braconid wasp have reached the pupal stage - indicated by the white rice-shaped cocoons which have been spun by the larvae. After pupation is complete the adult will emerge through an opening at the end of the cocoon. The hornworm may remain alive while the larvae pupate but it is unlikely to survive beyond their emergence.

Many species of parasitoid insects are considered beneficial because they attack many crop pest species such as aphids and various caterpillars.

Photo of Braconid wasp courtesy of R.J. Reynolds Tobacco Company Slide Set , R.J. Reynolds Tobacco Company. Image 1402142.