Manipulating your victim: the adaptive significance of host usurpation by the endoparasitoids Cotesia glomerata and Cotesia congregata

General information on earlier student projects below - updates with supervisor Jeff Harvey!

Parasitoid wasps are known to exhibit two strategies for exploiting host resources during development. The first is for the parasitoid larvae to consume the entire host (such as a caterpillar) before pupation. However, some parasitoids consume only a small fraction of the host during development. In this case, the mature parasitoid larvae emerge through the sides of the still-living host and pupate on, or next to it. In some instances, the caterpillar may remain alive for up to two weeks after parasitoid pupation and remain very close to the parasitoid cocoons.

A paper published in Animal Behavior (1995) by Jacques Brodeur and Louise Vet argued that the parasitized caterpillar sits and defends the parasitoid cocoons from predators and hyperparasitoids, acting as a surrogate ‘bodyguard’. Parasitized caterpillars were found to be more aggressive than non-parasitized ones. However, until now the hypothesis has received little experimental support, nor have the mechanisms been determined.

It has also been shown by Harvey and Tanaka (unpublished) that there are different types of ‘guarding’ behavior demonstrated by parasitized caterpillars. Some species, like the cabbage moth Pieris brassicae, sit on top of the clustered cocoons of its parasitoid Cotesia glomerata and the caterpillars behave aggressively when disturbed, but remain sessile. On the other hand, cocoons of the parasitoid Cotesia congregata remain attached to the caterpillar (the tobacco hornworm, Manduca sexta) host, but do not form a cluster. The caterpillar is very active after parasitism, and is also aggressive when disturbed.

This project will compare the effectiveness of these caterpillar defence strategies in protecting cocoons of both C. glomerata and C. congregata from their hyperparasitoid, Lysbia nana. This hyperparasitoid attacks cocoons of both primary parasitoid hosts, and thus experiments will be set up by the student in which caterpillars will be allowed to guard the cocoons or will be removed when L. nana females are present. The insects are currently cultured at Wageningen University and at the Netherlands Institute of Ecology. It is envisaged that the results will be written into a manuscript to be submitted to a peer-reviewed journal.

Contact information
Dr. Jeff Harvey, e-mail: j.harvey@nioo.knaw.nl