Edge by day, everywhere by night: Sentinel prey reveal spatiotemporal biocontrol patterns in Canadian prairie canola

• Sentinel prey used to quantify conservation biocontrol. • Diurnal and nocturnal pest egg predation differed strongly. • Elevated pest predation observed in the non-crop vegetation areas. • Higher pest predation observed during the night. • No evidence of predation spillover from non-crop vegetation. Anthropogenic impacts on terrestrial ecosystems are widespread, with land use change posing a major threat to biodiversity as natural and semi-natural areas are converted for agriculture and urban uses. Even in intensively managed agricultural landscapes, scattered remnants of biological diversity persist. These non-crop vegetation areas (NCVAs), often consisting of the small, grassy margins and ditches that surround monoculture crops, can act as biodiversity ‘hotspots’ that provide a refuge and source habitat for a broader community of beneficial arthropod species that can then spillover into crops, where they can provide ecosystem services such as biological control. The presence of insect predators in these areas does not directly translate to pest control as an ecosystem service. Sentinel prey, a measurable prey that is deployed in fields, allows for quantification of this service. In three canola fields, we sampled 20 stations to assess predation on sentinel prey, with separate trials for diurnal and nocturnal predation during three points in the canola growing season. During the day, sentinel prey results showed elevated observed predation in NCVAs, indicating they may be hotspots for pest predation. The observed increase overall in predation at night indicates the importance of nocturnal predators in conservation biocontrol. We found no evidence of spillover at the distances sampled; however, daytime predation was elevated in NCVAs and predation was higher overall at night, underscoring the importance of diel variation in biological control.