Generalist predators can provide important ecosystem services by reducing herbivore populations in agricultural systems. Effective biological control can increase plant yield and reduce the need of pesticide application, both being profitable for farmers. The present work investigated the impact of generalist predators on aphid populations in winter wheat, factors modulating these effects and tools helping to better understand predator-prey interactions. Improving habitats within and aside arable fields for generalist predators is of major concern in conservation biological control, therefore the first field experiment focused on the impact of detrital subsidy on herbivore suppression via increasing alternative prey from the detritivore subsystem. Carbon originating from maize mulch, applied shortly before winter wheat was sown, was incorporated by belowground decomposers as well as predators, indicating diverse trophic links in the belowground subsystem. Two aboveground generalist predators, one carabid and one staphylinid species, also incorporated maize-born carbon. These predators along with several other species were significantly increased by the addition of mulch material. Consequently, only in mulched fields aphid populations were significantly decreased. The results suggest linkages between the belowground and aboveground system via generalist predators, showing detrital subsidies to be a valuable tool to foster biological control. As these effects were not consistent between fields, additional factors as well as the temporal and spatial scale have to be considered in evaluating effects of detrital subsidies for biological control. The presence of alternative prey might distract generalist predators from the target prey; therefore, the second field experiment focused on the effect of generalist predators on aphid populations as well as on abundant alternative prey. Generalist predators decreased aphid densities below the threshold of economical damage even at high initial aphid density. Collembolans were also decreased by generalist predators irrespective of aphid density, indicating complementary predation of these two prey species. Moreover, generalist predators shifted from abundant belowground prey (click beetles) to aphid prey at increasing aphid densities. The results demonstrated non-disruptive effects of alternative prey on aphid suppression, supporting the idea of alternative prey enhancement for improving biological control. Abiotic factors can modulate predator-prey interactions, thereby modifying biological control. In a microcosm experiment the effect of rain on aphid predation by ground dwelling predators was analysed. Rain dislodged aphids from wheat plants, increasing aphid prey availability on the soil surface. Rain increased aphid consumption by ground dwelling predators. However, this did not affect aphid infestation, suggesting that the predators preferentially consumed dead aphids (scavenging). This was further addressed in a mesocosm experiment; all investigated generalist predators except a lycosid spider species fed on dead aphids proving that scavenging is common in carabids and staphylinids. For the analysis of the microcosm and mesocosm experiments an advanced DNA-based gut content analysis was employed, enabling accurate evaluation of trophic links. To improve the applicability of the technique, laboratory feeding trials were conducted to investigate factors affecting prey DNA detectability in predator guts. Effects of ambient temperatures below 20 °C did not affect prey DNA detectability, indicating that ambient temperature might be of minor importance for DNA gut content analysis. Testing detection rates of four different amplicon sizes, the largest and the shortest fragment significantly decreased and increased prey DNA detectability, respectively. Therefore, primer pairs amplifying fragments differing distinctly in amplicon size may be used to analyse both predation rates and the time when predation occurred. However, detection rates of prey DNA may vary even between closely related predator species.