Parasitic wasps

Most parasitoids control the behaviour of a particular host to benefit in defensive strategies for their larvae which is exactly what this parasitic wasp (Cotesia glomerata) does. The wasp not only alters the behaviour of the host but also physical and psychological patterns. The wasp is able to manipulate the host’s ability to construct shelters with intentions focused primarily in protecting larvae of the wasp (Edmunds 1974).

C. glomerata is involved in a parasitic relationship with host caterpillars in which the wasp injects its larvae into. The larvae are then able to feed on the host’s blood, whilst maintaining an interest in keeping the host alive avoiding any vital organs. At around 12 days the larvae start to become highly active in which they have developed specialised teeth that can slice through the tough skin of the caterpillar. The combined mass of the larvae can account for over a third of the caterpillar’s weight. In order to complete the next stage of the wasp’s life cycle they egress from the caterpillar’s body. Prior to exiting, the larvae release a toxin that temporarily paralyses the host. Once the larvae have exited the host, they begin to spin silk cocoons which provide an adequate environment for their final stages of development. These larvae are subject to hyperparasitoids which are parasites that host on other species of parasite. In this particular case, other species of parasitic wasp are able to use the larvae as hosts in which another feature of this intriguing relationship kicks in (Tanaka and Ohsaki, 2006).

Figure 1. Photographer: Paul M (2006). Caterpillar of Pieris brassicae guarding the larvae of Cotesia glomerata.

The host is not killed in the process of the larvae exiting, instead its behaviour has changed and seems to help and protect the young larvae. The caterpillar spins an additional silk layer over the group of cocoons for added protection and camouflage to other parasitoids. The caterpillar tends to the cocoons in an attempt to ensure their survival in which it eventually starves itself to death (Karowe and Schoonhoven, 1992).

This relationship is an interesting example of parasitism on multiple levels, in which it alters its host’s physical, psychological and behavioural characteristics which ultimately benefit the wasp’s biological fitness and reproductive success.

Video with thanks to National Geographic 

https://www.youtube.com/watch?v=vMG-LWyNcAs

References:

Edmunds M (1974) Defence in animals. A survey of anti-predator defences. Longman, New York

KAROWE, D. & SCHOONHOVEN, L. 1992. Interactions among three trophic levels: the influence of host plant on performance of Pieris brassicae and its parasitoid, Cotesia glomerata. Entomologia experimentalis et applicata, 62, 241-251.

TANAKA, S. & OHSAKI, N. 2006. Behavioral manipulation of host caterpillars by the primary parasitoid wasp Cotesia glomerata (L.) to construct defensive webs against hyperparasitism. Ecological Research, 21, 570-577.

Figure 1. Paul M (2006). Caterpillar of Pieris brassicae guarding the larvae of Cotesia glomerata.