F. L. Wäckers, P.C.J. van Rijn and J. Bruin, eds.
Cambridge University Press
Cambridge, 2005, 356 pp., $130.00
ISBN: 0-21-81941-5

Plant-herbivore interactions, trophic cascades, and tritrophic relationships are nonrandom associations that have been the subject of much interest among evolutionary and ecological entomologists. Issues such as evolutionary pathways of plant-insect relationships, chemical mechanisms responsible for these relationships, and their population-, community-, and ecosystem-level consequences have captivated researchers' interest not only for their basic ecological implications, but also for their importance in applied areas such as biological control. In this context, Plant-Provided Food for Carnivorous Insects: A Protective Mutualism and Its Applications provides a novel perspective on plant-herbivore-carnivore relationships. Instead of emphasizing the influence that plants and herbivores have on carnivores, this book focuses on the environmental requirements, evolutionary pathways, and ecological functions of the natural enemies themselves.

This book is organized in an introductory chapter and three sections. The first section is comprised of three chapters that emphasize the resources provided by plants, as well as the evolutionary ecology of plant-insect interactions. The first chapter of this section provides a comprehensive review of the physical and chemical characteristics of different types of plant-provided food as well as the factors that can affect their suitability for omnivores. This chapter provides much of the information needed to critically evaluate the potential use of food supplements to increase the effectiveness of predators and parasitoids in suppressing prey populations. The last two chapters of this section examine hypotheses and associated evidences that food-for-protection mutualisms are widespread patterns and that they provide important fitness consequences to plants. However, some of the evidence cited, as well as the lack of information regarding other aspects of the evolution of these mutualisms (such as their persistence in the face of potential exploitation), suggest that that there is still much room for additional theoretical and empirical studies.

The second section of the book focuses on arthropods' feeding habits. Overall, these chapters highlight that high-nitrogen food resources such as pollen, seeds, and pods can have a large impact on omnivore arthropod populations. With much detail, these chapters describe how the quantity, quality, and accessibility of food resources interact with natural enemies behavioral patterns and morphological structures. They further explore how these resources impact plant-omnivore-prey dynamics. As the authors point out, little is known about the mechanisms by which these interactions occur. Unfortunately, for the most part, this section fails to provide a comprehensive list of research questions demanding additional studies. However, the authors do recommend a few areas ripe for further research, including quantifying the effect of plant feeding on omnivore-prey interactions, understanding the functional and numerical response of omnivorous predators, and comparing the relative impact of strict predators versus omnivores in suppressing prey populations. Ultimately, answering these questions will provide the necessary knowledge to design applied biological control programs based on the functional importance of biodiversity.

The third section of the book is comprised of four papers on the importance of plant-provided food for biological control with examples of how habitat diversification could enhance the survivorship of beneficial insects in highly simplified and disturbed settings such as modern agroecosystems. Although appealing, the concept that habitat management can be used to promote natural enemies of agricultural pests is not a new one and has been previously discussed in other books (Barbosa 1998, Pickett and Bugg 1998, Hawkins and Cornell 1999). Consequently, little in this section could be considered new information. The most novel contribution in this section is the chapter by Gurr and collaborators that critically review ecological theory to improve conservation biological control, pointing out that a "shotgun approach" to enhance habitat diversity could result in unintended negative consequences. They further suggest that in agricultural systems, the use of mathematical modeling, and risk analysis are valid means to increase the success rate of conservation biological control programs.

This book is a timely review for entomologists and biological control specialists interested in the evolutionary and ecological importance of omnivorous multitrophic interactions. Its exhaustive literature review could be helpful to graduate students and researchers interested in food-web ecology in both natural and managed systems. Unfortunately, it is often left up to the reader to figure out where the most productive future research questions are.

References
Conservation biological control. P Barbosa, ed. New York, Academic, 1998.

Theoretical approaches to biological control. B. A Hawkins, H. W Cornell, ed. Cambridge, Cambridge University Press, 1999.

Enhancing biological control. Habitat management to promote natural enemies of agricultural pests. C. H Pickett, R. L Bugg, ed. Berkley, CA, University of California Press, 1998.

Fabian D. Menalled and Richard G. Smith
Department of Land Resources and Environmental Sciences
Montana State University
Bozeman, Montana

Environmental Entomology
Vol. 35, No. 4, August 2006, Page 1137