Plant-Provided Food for Carnivorous Insects: a Protective Mutualism and Its Applications

PlantÐherbivore 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 plantÐinsect relationships, chemical mechanisms responsible for these relationships, and their population-, community-, and ecosystem-level consequences have captivated researchersÕ interest not only for their basic ecological implications, but also for their importance in applied areas such as biological control. In this context, PlantProvided Food for Carnivorous Insects: A Protective Mutualism and Its Applications provides a novel perspective on plantÐherbivoreÐcarnivore relationships. Instead of emphasizing the inßuence 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 Þrst section is comprised of three chapters that emphasize the resources provided by plants, as well as the evolutionary ecology of plantÐ insect interactions. The Þrst chapter of this section provides a comprehensive review of the physical and chemical characteristics of different types of plantprovided 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 Þtness 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 arthropodsÕ 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 plantÐomnivoreÐprey 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 omnivoreÐprey 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 diversiÞcation could enhance the survivorship of beneÞcial insects in highly simpliÞed 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. Themostnovelcontribution inthis section is thechapter 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, theuseofmathematicalmodeling, andriskanalysis 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 Þgure out where the most productive future research questions are.