LAUSR

Rosenheim et al. (1) present an interesting study testing the effect of focal field size on pest suppression across multiple cropping systems. The main conclusion of their study is “The idea that larger field sizes consistently disrupt natural pest control services is without foundation in either the theoret - ical or empirical record.” We argue that this general conclu - sion should be considered with more caution. First, Rosenheim et al. focused on the local effect of field size com - paring pest density in small vs. large fields irrespective of the configuration of the surrounding landscape. However, most of the empirical research providing evidence for a positive effect of reducing field size on pest suppression or natu - ral-enemy enhancement has tested the effect of landscape configuration (e.g., gradients in field size or edge density in the surrounding), usually adopting specific designs to control for differences in landscape composition (2–5). Decreasing field size at the landscape scale is expected to have more pervasive effects than the size of the focal field alone. Fine-grained landscapes usually have a higher density of margins and higher microhabitat diversity, resulting in improved land - scape complementation and in the facilitation of spill-over of organisms between crop and noncrop patches (6). This scale dependence was not fully acknowledged in the study, generating confusion between the reported lack of a local effect and the potential—but not investigated—effect of reducing mean field size at larger spatial scales. Second, the data used (1) come from unplanned field obser - vations by farm staff, consultants, and pest control advisors who quantified pest pressures without any sampling design. As pest suppression is often context dependent, many poten - tial biotic and abiotic drivers of success or failure exist (7, 8). Without a robust design, observational landscape studies usu