Adaptive Value

The adaptive value of parasitism for the Ampulicidae family is multifold.  As in all parasitic relationships, Ampulex compressa uses its host, the cockroach, as an energy source.  Rather than putting resources towards the creation of shelter and the gathering of food for larvae, the female wasp relies on her host as a source of both, while channeling all of her energetic efforts towards the creation of a healthy egg. Unlike an endoparasite, exoparasitic wasps rely on hosts only for the rearing of offspring and in the absence of a suitable host, larvae can still survive and develop to maturity. (Libersat 2009)

Creating a Resistance-Free Host

What makes this parasitic relationship unique is the neurological control of the host induced by the wasp’s venom.  A cockroach on its own would not be a suitable habitat for larval incubation; its larger size, faster speed, and its own reproductive goals make it resistant to attacks.  Successful stings, however, render the cockroach resistance-free and in the perfect position for the wasp and her larva to reap the energetic benefits.  This resistance-free relationship is presumably ideal for a host-parasite interaction, yet many parasites don’t have such control over their hosts.  The recently-developed evolutionary advantage conferred by a complex neurological command mechanism is shown by the wasp's widespread success in multiple environmental situations.

How this specified venom delivery behavior evolved is still a mystery. In most related Sphecid wasps, muscle paralysis is the only mechanism of host control. Ampulex compressa, however, induces only brief paralysis in host musculature in order to access the cerebral ganglia and uses this neurological mechanism as the primary means for host control. It has been suggested that natural selection among individuals of this species has led to the development of such a direct stinging mechanism, the advantage being less energy expenditure from transportation of the host to the burrow (the cockroach essentially walks itself there). (Gal et al 2005).


parasite life cyclePerhaps the primary reproductive value of this wasp species’ parasitic behavior is that of “free” oviposition.  By laying the egg inside the cockroach, the wasp mother does not have to worry about tending to her developing larva; everything the larva needs is held within the host organism and is kept alive long enough to provide for the larva without the mother’s intervention.  A huge energetic burden is thus lifted from the mother’s shoulders. (Figure 8. Aphid parasitoid life cycle. Photo source 4)