This volume is a revision of Biological Control by R. van den Bosch and P. S. Messenger, originally published by Intext Publishers. In the revision, I have attempted to keep the original theme, and to update it with current research findings and new chapters or sections on insect pathology, microbial control of weeds and plant pathogens, population dynamics, integrated pest management, and economics. The book was written as an undergraduate text, and not as a complete review of the subject area. Various more comprehen sive volumes have been written to serve as handbooks for the experts. This book is designed to provide a concise overview of the complex and valuable field of biological control and to show the relationships to the developing concepts of integrated pest management. Population regulation of pests by natural enemies is the major theme of the book, but other biological methods of pest control are also discussed. The chapter on population dynamics assumes a precalculus-levelknowledge of mathematics. Author names of species are listed only once in the text, but all are listed in the Appendix. Any errors or omissions in this volume are my sole responsibility. A. P. Gutierrez Professor of Entomology Division of Biological Control University of California, Berkeley vii Acknowledgments Very special thanks must be given to my colleagues, Professors C. B. Huffaker and L. E. Caltagirone, for the very thorough review they provided and for the many positive suggestions they gave. Dr.