 of years of co-evolution have driven parasites to display very complex and exquisite strategies to manipulate the behaviour of their hosts. However, although parasite-induced behavioural manipulation is a widespread phenomenon, the underlying neuronal mechanisms are only now beginning to be deciphered. Here, we review recent advancements in the study of the mechanisms by which parasitoid wasps use chemical warfare to manipulate the behaviour of their insect hosts. We focus on a particular case study in which a parasitoid wasp (the jewel wasp Ampulex compressa) performs a delicate brain surgery on its prey (the American cockroach Periplaneta americana) to take away its motivation to initiate locomotion. Following a brief background account of parasitoid wasps that manipulate host behaviour, we survey specific aspects of the unique effects of the A. compressa venom on the regulation of spontaneous and evoked behaviour in the cockroach host.(Big awesome post about parasitoid wasps previously: The players in a mutualistic symbiosis: insects, bacteria, viruses, and virulence genes.)Comparing mechanisms of host manipulation across host and parasite taxa
Parasites affect host behavior in several ways. They can alter activity, microhabitats or both. For trophically transmitted parasites (the focus of our study), decreased activity might impair the ability of hosts to respond to final-host predators, and increased activity and altered microhabitat choice might increase contact rates between hosts and final-host predators. In an analysis of trophically transmitted parasites, more parasite groups altered activity than altered microhabitat choice. Parasites that infected vertebrates were more likely to impair the host’s reaction to predators, whereas parasites that infected invertebrates were more likely to increase the host’s contact with predators. The site of infection might affect how parasites manipulate their hosts. For instance, parasites in the central nervous system seem particularly suited to manipulating host behavior. Manipulative parasites commonly occupy the body cavity, muscles and central nervous systems of their hosts. Acanthocephalans in the data set differed from other taxa in that they occurred exclusively in the body cavity of invertebrates. In addition, they were more likely to alter microhabitat choice than activity. Parasites in the body cavity (across parasite types) were more likely to be associated with increased host contact with predators. Parasites can manipulate the host through energetic drain, but most parasites use more sophisticated means. For instance, parasites target four physiological systems that shape behavior in both invertebrates and vertebrates: neural, endocrine, neuromodulatory and immunomodulatory. The interconnections between these systems make it difficult to isolate specific mechanisms of host behavioral manipulation.
Parasite-induced alterations of sensorimotor pathways in gammarids: collateral damage of neuroinflammation?TOXOPLASMOSIS
Some larval helminths alter the behavior of their intermediate hosts in ways that favor the predation of infected hosts, thus enhancing trophic transmission. Gammarids (Crustacea: Amphipoda) offer unique advantages for the study of the proximate factors mediating parasite-induced behavioral changes. Indeed, amphipods infected by distantly related worms (acanthocephalans, cestodes and trematodes) encysted in different microhabitats within their hosts (hemocoel, brain) present comparable, chronic, behavioral pathologies. In order to evaluate the potential connection between behavioral disturbances and immune responses in parasitized gammarids, this Review surveys the literature bearing on sensorimotor pathway dysfunctions in infected hosts, on the involvement of the neuromodulator serotonin in altered responses to environmental stimuli, and on systemic and neural innate immunity in arthropods. Hemocyte concentration and phenoloxidase activity associated with melanotic encapsulation are depressed in acanthocephalan-manipulated gammarids. However, other 