Introduction

The need for a theoretical foundation to biological control has often been emphasized (Waage 1990; DeBach and Rosen 1991; Ehler 1994; Sheehan 1994; Barbosa 1998; Gurr et al. 1998; Wratten et al. 1998; Berryman 1999; Hawkins and Cornell 1999; Landis et al. 2000). Enhancement of natural enemy efficacy with floral resources provides a perfect opportunity for this kind of input; however, a divide exists between ecological principles and the needs of practical agriculture. In order for advances in theory to be utilized, protocols based on both ecology and agricultural realism are needed. Partial information, based on anecdote, may lead to the accidental introduction of noxious weeds, and the enhancement of pest populations (Baggen and Gurr 1998) or higher-order predators/hyperparasitoids (Stephens et al. 1998). Thus the introduction of non-crop plants as nectar and pollen sources has the potential to cause harm as well as to provide benefits (see also Wilkinson and Landis, Chapter 10). Practical guidelines for employing plant foods in farming systems must be based on sound theoretical and empirical foundations, yet be easily integrated into agricultural and horticultural practice.

We review the ways in which researchers, as well as agronomists and farmers, have attempted to provide plant foods to natural enemies of pests. We discuss the various approaches to the use of flowering plants, and draw a distinction between “shotgun” and “directed” approaches.