Sentinel prey settings differ in their ability to distinguish organic from conventional apple orchards and in their sensitivity to weather conditions during field exposure

• Monitoring of the predation of four sentinel prey for nine years in orchards. • Sentinel prey were more informative when exposed in the canopy than on the ground. • Correlated predation of aphids and Ephestia kuehniella eggs in the tree canopy. • Higher predation of aphids and lepidoptera eggs but not seeds in organic orchards. • Ephestia eggs are good candidate sentinel prey for large-scale studies. Determining factors that affect pest predation by natural enemies is essential for designing cropping systems that promote conservation biological control. Predation of sentinel prey has become an increasingly popular measure of predator activity for comparing fields with differing characteristics of interest. However, many different sentinel prey exist, and such studies rarely examine how the specific prey used influences their conclusions, especially in perennial crops. We compared the ability of four sentinel prey, placed either in the tree canopy (eggs of two Lepidoptera, Cydia pomonella and Ephestia kuehniella , and aphids, Acyrthosiphon pisum ) or on the ground (aphids, A. pisum , and seeds of Viola arvensis ), to differentiate between organic and conventional apple orchards. Furthermore, we assessed whether their predation depended on weather conditions during field exposure. We monitored predation of these sentinel prey during two field sessions (April and May) over nine years in 14 apple orchards. Predation of aphids exposed for 24 h on the ground was always high. Predation of all other prey, except seeds, was higher in organic than in conventional orchards, particularly during the April field session. Additionally, the predation of seeds, and to a lesser extent of aphids, was influenced by weather conditions during exposure. Ephestia eggs emerged as a suitable choice for comparing predation by generalist predators among orchards, as they were easy to handle and their predation rates were positively correlated with those of aphids exposed in the tree canopy. Codling moth eggs displayed a somewhat different predation pattern and could be a valuable complement.