Tritrophic

In the context of tritrophic interactions, plant-plant communication has been subject to only few studies (Bruin et al., 1995). In one such study, Bruin et al. (1992) demonstrated that healthy cotton plants that were exposed to spider mite-induced volatiles from conspecihc plants increased in their attractiveness to predatory mites. This increased attraction was probably not simply the result of adsorbence and re-release of these volatiles from the healthy plants, because there is now clear evidence that volatiles from spider mite-infested plants can induce odor releases in neighboring plants (Arimura et al, 2000a). 

Although much is known about various intricacies of the active role of plants in tritrophic interactions, it is evident from the above review that numerous questions remain and several areas are virtually unexplored. We identify three areas that appear to us as particularly interesting and they can be expected to receive special attention in future research programs. 

Agelopoulos, N. A. and Keller, M. A. (1994). Plant-natural enemy association in the tritrophic system Cotesia rubecula-Pieris rapae-Brassicaceae (Cruciferae). Ill Collection and identification of plant and trass volatile. Journal of Chemical Ecology 20 1955-1967. 

Gomez, J. M. and Zamora, R. (1994). Top-down effects in a tritrophic system parasitoids enhance plant fitness. Ecology 75 1023-1030. 

Hare, J. D. (2002). Plant genetic variation in tritrophic interactions. In Multitrophic Level Interactions, eds. T. Tscharntke and B. A. Hawkins, pp. 8 13. Cambridge Cambridge University Press. 

Shiojiri, K., Takabayashi, J., Yano, S. and Takafuji, A. (2001). Infochemically mediated tritrophic interaction webs on cabbage plants. Population Ecology 43 23-29. 

Oviposition preferences of herbivores are affected by tritrophic interaction webs. Ecology Letters 5 186-192. 

Chapters in this volume consider how plants use chemicals to defend themselves from insect herbivores the complexity of floral odors that mediate insect pollination tritrophic interactions of plants, herbivores, and parasitoids, and the chemical cues that parasitoids use to find their herbivore hosts the semiochemically mediated behaviors of mites pheromone communication in spiders and cockroaches the ecological dependence of tiger moths on the chemistry of their host plants and the selective forces that shape the pheromone communication channel of moths. 

In many recent studies, the role of terpenoids in indirect defense has been studied. A broad range of plant species such as Arabidopsis, com, lima bean, cucumber, tomato, tobacco, apple, and poplar serves as models for studies on the genetic, biochemical, physiological, and ecological aspects of these tritrophic interactions between plants, herbivores, and natural enemies (e.g.. Reference 10). Plants have been shown to respond with quantitatively and qualitatively different volatile blends to different herbivore species, and predators can exploit this behavior to respond specifically to their prey (Fig. 3)... 

Tritrophic interactions, for which so much evidence exists aboveground, are gradually being uncovered in the rhizosphere... 

The role of benzoxazinoids, namely of DIMBOA, in com resistance against a number of pests was reviewed several times during the last years. Therefore, this aspect is not further considered except for an interesting tritrophic interaction. 

Semiochemicals can be placed into two distinct classes Pheromones control intraspecific interactions. These semiochemicals provide information regarding a range of behaviours including mate selection, aggregation, dispersal (alarm pheromones), oviposition and food sources (trail pheromones). Allelochemicals control interspecific interactions such as host and non-host identification by primary colonizers (plant or animal) and whether a food source is already exploited through tritrophic interactions (signals indicating the presence of primary colonizers). 

We have incorporated this hypothesis into Fig. 4.14, which is an expanded tritrophic version of Fig. 4.9. The top of this diagram now includes feedback between tunneling, which elicits oxygenated terpene and monoterpene emission and resulting arrival by predators and competitors, and impacts of these predators and competitors on beetle reproduction. Both of these relationships are well supported in the literature. " However, this model also proposes that the spatial and temporal patterns of host availability, in terms of both compromised tree defenses and beetle perception of these alterations, affect natural enemy numbers. Natural enemy populations in turn affect beetle population size, which in turn affects host acceptance behavior (Fig. 4.14 center). 

Our specific conclusions are 1) Individual compounds can affect interactions across multiple levels of scale, from molecular through landscape 2) At each level of scale, the same compounds can be sources of both positive and negative feedback. Their interactions across scales can be amplified or buffered, depending on these feedback processes 3) Host selection behavior can be an important link between physiological and population processes, particularly where responses to phytochemicals are plastic 4) Tritrophic interactions mediated by chemical cues can be either important or ineffective constraints on eruptive behavior, depending on how prey are spatially and temporally distributed, which in turn reflects their host... 

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