Successful conservation biological control: In search of the holy agroecological grail?

Background/Question/Methods In the past decade, at least 23 field studies have tested the hypothesis that enriching agroecosystems with floral resources will enhance biological control of agricultural pests.  Less than a third of those studies consistently found a positive effect of added floral subsidies on parasitism or predation in the field, while almost half showed mixed results and a quarter showed no effect at all.  On the other hand, laboratory studies have consistently shown that natural enemy longevity and fecundity are positively related to floral subsidies. It is clear that floral habitat enhancements are attracting, supporting, and improving the fitness of natural enemies-- much less clear is how added floral subsidies affect natural enemy behavior in the field. This presentation reviews the findings on conservation biological control (CBC) field research over the past ten years, a period of marked growth in CBC research.

Results/Conclusions The interactions between flowering plant, natural enemy, herbivore, and crop plant are inherently complex. We discuss the influence of variables including intra-field diversity, landscape complexity, and scale of movement on localized biological control. The assumption that if parasitoid and predator populations are enhanced, they will be more active (i.e. attack pests of agricultural importance) in crop fields may not be a reliable one.  Successful CBC programs depend upon a better understanding of the biology of the natural enemies and their fidelity to particular plants and host prey. We propose ways forward in CBC research that may improve our ability to predict pest control from habitat enhancements.