interactions. Concerns related to multispecies and multitrophic interactions are leading to some experimentation and field applications.

• Plant pathologists are infecting plants with certain minor pathogens that protect the plants from more devastating pathogens.

• Weed scientists are investigating how the interactions of a crop infested with multiple species of weeds affect yield.

• Research teams are discovering higher concentrations of beneficial organism attractants in wild plants than in their commercial counterparts.

The knowledge base in this area has expanded in the past decade, but a complete understanding of such multitrophic-level interactions is essential for designing effective and reliable biological-control measures for EBPM.

The mechanisms that govern interactions among organisms have been an area of intense study in both medical and agricultural research because understanding these mechanisms is key to understanding how pests and diseases can be controlled through active intervention. For agriculture, one of the pay-offs of such knowledge would be the ability to quickly develop genetically engineered plants resistant to pests. Already the toxins responsible for the success of Bacillus thuringiensis (Bt) as a biological-control agent offer promise for the enhancement of plant resistance to specific arthropods when the genes encoding the toxins are incorporated into plant genomes.

Knowing what factors control interactions among organisms will help scientists better understand how to manipulate pest populations, or communities containing these organisms, to reduce their impact. Understanding biological control at the cellular or molecular level has a predictive value, enabling scientists to set realistic expectations for when and where biological control may succeed or fail. For example, if biological control is known to be mediated by iron competition between an antagonist and a target pathogen, it is not likely to succeed in conditions in which iron is replete. Identification of the characteristics that determine biological-control activity is prerequisite to manipulating these characteristics through genetics, modification of behavior or the environment, or other interventions.

The discussion of research needs in the following section provides suggestions as to how additional knowledge of processes directly related to biological control can be used to enhance biological-control processes. The committee's recommendations are meant to focus on gaps in current research priorities that are uniquely related to biological-control issues. Although there have been some major developments in studies of plant-host interactions (e.g., the finding that a specific plant host, by cellular signaling, indicates recognition of a pathogen),