Presents the first efforts to explore ecological interactions between insects and plants across several trophic levels, with special focus on mediation of complex interactions by plant allelochemicals. First section looks at effects of plant allelochemicals on predator-prey and host-parasitoid interactions. Second section reveals the role of microorganisms as mediators of interactions between insects and plants. Third section unifies and extends current theory to examine the effects of allelochemicals on the second and third trophic levels. Final section traces the physiological effects of plant allelochemicals in animal behavior, population regulation, maintenance of mimicry systems, and evolution of host range.