Plant-insect interaction Herbivore defense

Hay ME, Duffy JE, Fenical W (1990) Host-plant specialization decreases predation on a marine amphipod an herbivore in plant s clothing. Ecology 71 733-743 Hay ME, Duffy JE, Pfister CA, Fenical W (1987) Chemical defense against different marine herbivores are amphipods insect equivalents Ecology 68 1567-1580 Hay ME, Fenical W (1992) Chemical mediation of seaweed-herbivore interactions. In John DM, Hawkins SJ, Price JH (eds) Plant-animal interactions in the marine benthos. Clarendon, Oxford, pp 319-337... 

Rhoades, D. F., Offensive-defensive interactions between insects and plants their relevance in herbivore population dynamics and ecological theory, Am. Nat., 125, 205, 1985. 

A comparable situation to insect specialists can be found in parasitic and hemi-parasitic plants, another example of multitrophic interactions. In several instances it can be shown that the parasites can tap the xylem or phloem of their host plants and sequester the host alkaloids into their own system [2,31]. The parasites would gain chemical defense against herbivores by such a process (Table 1.4). In Osyris alba it can be shown that plants exist that can sequester the alkaloids of more than one host plant that is, pyrrolizidine and quinolizidine alkaloids [32]. The situation of Lolium is even more complex [33]. If the grass Lolium temulentum is infected by an endophytic... 

Over 20,000 terpenoids have been identihed (1), and more are being discovered continuously. Plant terpenoids are important in both primary and secondary (speciahzed) metabolism. Their importance in primary metabolism includes physiological, metabolic, and stmctural roles such as plant hormones, chloro-plast pigments, roles in electron transport systems, and roles in the posttranslational modihcation of proteins. In secondary metabolism, the roles of plant terpenoids are incredibly diverse but are associated most often with defense and communication of sessile plants interacting with other organisms. Examples include terpenoid chemicals that form physical and chemical barriers, antibiotics, phytoalexins, repellents and antifeedants against insects and other herbivores, toxins, attractants for pollinators or fruit-dispersing animals, host/nonhost selection cues for herbivores, and mediators of plant-plant and mycorrhiza interactions (2, 3). 

Plant sesquiterpenes and other terpenoids aie major detenninants of insect-plant interactions (2i 16V Many insecticidal and antifeedant terpenoids are epoxides including monoteipene Q2, 18. sesquiteipene QQ, 19-23). diteipene (Jl, 24) and triteipene derivatives (25-27) typified by the potent antifeedant azadirachtin (28-30). Most biolo cal effects have been determined with Lepidoptera and non-chrysomelid Coleoptera. Occasionally, the same compound, while normally inhibitory to herbivores, may for adapted insect species or at low concentrations have a stimulatory effect (13). Insects, in turn, synthesize their own defensive (21, and pheromonal (22) terpenoids. Plants may utilize insect pheromones such as the sesquiterpene alarm pheromone, rranj-B-famesene, in their own defense (34. 35). Inhibitory cyclic sesquiterpenes (Table I) and diterpenes (Table II) for insect herbivores have been identified from at least 28 genera of the terpenoid-rich Compositae. These studies were largely confined to extrafloral tissues. 

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