Biotic Stress and Yield Loss

plant buffering mechanisms, then use of individual leaves should provide a moredetailed understanding.”Describing how individual leaves respond to injury is important given that theseare the organs most immediately affected by herbivory. This is reflected in the literature;the research area on plant gas exchange and herbivory is replete with papers onindividual leaf responses to herbivory. 1 However, describing leaf gas exchangeresponses to injury clearly is not sufficient. Developing a more complete understandingof injury requires that greater attention be given to responses at organizationallevels above and below that of individual leaves. Mechanistic understanding ofgas exchange responses necessitates work at lower levels of organization (e.g.,molecular and cellular levels). The Mexican bean beetle example discussed above isan example of research at these levels of biological organization.In a similar vein, evolutionary, ecological, and agricultural understandings of theimpact of herbivory depend upon characterizing how plant populations are affectedby insect injury. Unfortunately, responses of individual leaves have not been relatedto responses at higher levels of organization. Indeed, I am aware of only four studiesdirectly examining canopy responses to herbivory.12, 13, 18, 336.2.2.2 Extrinsic FactorsBy determining the direct responses of insect injury on plant physiology, interactiveeffects can be evaluated more accurately (Figure 6.3). This is especially salient innatural systems because extrinsic factors constraining optimal plant growth, bothStress XArthropodInjuryInteractionResponseStress YStress XArthropodInjuryResponseInteractionResponseStress YFIGURE 6.3 Arthropod injury interacts with other biotic and abiotic stresses to produceplant responses (top). Substantial progress will be made by first characterizing the directresponses of plants to arthropod injury, and then determining how extrinsic factors interactwith arthropod stress (bottom).