Annu. Rev. Entomol. 2002. 47:817–44 Copyright c  2002 by Annual Reviews. All rights reserved HOST PLANT QUALITY AND FECUNDITY IN HERBIVOROUS INSECTS Caroline S. Awmack 1 and Simon R. Leather 2 1 Department of Entomology, 237 Russell Labs, 1630 Linden Drive, University of Wisconsin-Madison, Madison, Wisconsin 53706; e-mail: awmack@entomology.wisc.edu 2 Department of Biology and NERC Centre for Population Biology, Imperial College, Silwood Park, Ascot, Berkshire, SL5 7PY, United Kingdom; e-mail: s.leather@ic.ac.uk Key Words herbivory, offspring size, oviposition preferences, larval performance, nutrients, defensive metabolites ■ Abstract Host plant quality is a key determinant of the fecundity of herbivorous insects. Components of host plant quality (such as carbon, nitrogen, and defensive metabolites) directly affect potential and achieved herbivore fecundity. The responses of insect herbivores to changes in host plant quality vary within and between feeding guilds. Host plant quality also affects insect reproductive strategies: Egg size and quality, the allocation of resources to eggs, and the choice of oviposition sites may all be influenced by plant quality, as may egg or embryo resorption on poor-quality hosts. Many insect herbivores change the quality of their host plants, affecting both inter- and intraspecific interactions. Higher–trophic level interactions, such as the performance of predators and parasitoids, may also be affected by host plant quality. We conclude that host plant quality affects the fecundity of herbivorous insects at both the individual and the population scale. CONTENTS PERSPECTIVES AND OVERVIEW ...................................... 818 FECUNDITY AND OTHER MEASURES OF INSECT PERFORMANCE ............................................. 818 DIRECT EFFECTS OF DIET ON INSECT FECUNDITY ..................... 820 Nutritional Components of Diet Quality .................................. 820 Defensive Compounds and Their Effects on Insect Fecundity ................. 825 EFFECTS OF HOST PLANT QUALITY ON INSECT REPRODUCTIVE STRATEGIES ....................................... 828 MODIFICATION OF HOST PLANT QUALITY BY OTHER INSECT HERBIVORES .................................... 830 THE INTERACTIONS BETWEEN HOST PLANT QUALITY, HERBIVORES, AND NATURAL ENEMIES .............................. 832 CONCLUDING REMARKS ............................................ 833 0066-4170/02/0101-0817$14.00 817