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