Evolution parasitoid-host

The great diversity of parasitoids and the complexity of parasitoid-host relationships is probably influenced by attempts of potential host insects to escape their predators, parasites and parasitoids. There is considerable speculation on the role that parasites (parasitoids) play in herbivore evolution. There are many examples where a host on different plants is attacked by different parasitoid species (see Vinson, 1981). As discussed by Zwolfer and Kraus (1957), and Vinson (1981), plants play an important role in the host selection process, probably by providing cues to the location of a potential host community. Theoretically, a host could escape a particular parasitoid by attacking a plant lacking those stimuli used by the parasitoid to locate the potential host community. This idea is supported by the observation that there is less tendency for parasitoids to select phylogenetically related hosts than to favor a range of hosts on a particular plant (Askew and Shaw, 1978 Cross and Chesnut, 1971). 

One outstanding question that comes to mind when one describes the role kairomones play in host selection is why the host continues to produce the kairomone. No doubt elimination of the kairomone has occurred many times during the evolution of a parasitoid-host relationship, but proving such an alteration is very difficult. Most, if not all, kairomones probably serve the host in some essential way. For example, the mandibular gland secretion that acts as... 

There is little doubt that chemicals play an important role in the internal defense and counterdefenses that have evolved during the evolution of the various parasitoid-host relationships. Currently too little is known about the chemicals involved in internal recognition and defense to develop any overall concepts. 

The co-evolution implied in the parasitoid-host relationship does not stop once a host has been attacked, but continues as the progeny develop within or on the host. The growih, development, physiology, and behavior of the host is... 

All of the long-range kairomones attractive to parasitoids that have been identified thus far are sex pheromones of the hosts. However, we are probably aware of only a small fraction of the predators and parasites that are eavesdropping on the pheromonal communications of their prey or hosts. While the evolution of individuals that are as inconspicuous as possible to their enemies is favored, it is impossible for a species to completely avoid emitting chemical signals. Thus, pheromones that are important to reproduction or other vital functions, and are good indicators of the presence of a species, are available for predators or parasitoids to exploit. 

Shaw SR. Euphorine phylogeny the evolution of diversity in host-utilization by parasitoid wasps (Hymenoptera Braconidae). Ecol Entomol 13 323-335, 1988. 

The potential host community can be perceived by parasitoids through any of the above stimuli from the host, the food or shelter of the host, organisms associated with the host, or interactions between these factors. Plants appear to play an important role in potential host community location, partly because plants are the source of food for most hosts. It has been contended that the evolution of the parasitoid habitat in Hymenoptera may have stemmed from a previous plant-parasite relationship (Malyshev, 1968). If true, such a relationship would provide insight into the role of plants in the host selection process. The importance of plants in host community location is further supported by the observation that there is less tendency for parasitoids to select phylogen-etically related hosts than unrelated hosts found on the same plant (Cross and Chesnut, 1971). 

Fritz, R. S. (1982) Selection for host behavior modification by parasitoids. Evolution, 36, 283-8. 

---