Insect predators have been utilized in agroecosystems to reduce density of herbivorous pest damage on plants since the advent of agriculture. In addition to direct benefits to crops through consuming prey (a type of density-mediated indirect effect), predator presence can also indirectly benefit crops via risk-induced trait responses on prey behavior and physiology (a type of trait-mediated indirect effect, TMIE). These predation risk effects have been shown in several agriculturally relevant insect systems. Yet, the majority of examples come from studies performed in a laboratory setting and over small spatial and temporal scales (reviewed in Hermann and Landis 2017). Without data collected at realistic scales, it will remain exceedingly difficult to predict how predation risk effects function across managed landscapes to influence pest pressure. Examining the importance of predation risk effects in the field is particularly important if we aim to harness them to improve pest suppression and limit TMIE on crop plants. Recent research indicates that chemical cues of predatory insects allow prey to detect and respond to predation risk and these isolated predator cues can be used in agroecological experiments to create areas of ‘risk’ in a field setting. This set of studies aimed to investigate the potential for important agricultural predators, or their chemical cues, to elicit predation risk effects in the open field. Specifically, we assessed how predation risk influenced critical behaviors such as field colonization, host use and oviposition by experimentally manipulating predator presence or predator odor cues in field plots and compared these to unmanipulated control plots. We also analyzed the impact of predators or their cues on end of season plant biomass as a measure for TMIEs on crop yield.
Results/Conclusions
In a potato agroecosystem, predator cues did not influence pest colonization but subsequent feeding damage in plots with predator cues was significantly reduced compared to controls which in turn provided a yield benefit. When we performed a similar experiment on collard plants, colonization by the major pest in the systems was not influenced by predators or their cues. Unsurprisingly, end of season yield was unaffected by the treatments in this system. However, colonization of the collard plants by a secondary pest was negatively impacted by the predator treatments indicating that a more wholistic, community-wide approach should be used. These studies have allowed us to fine tune our manipulations and measurements for future studies in this exciting area of research.