Prey to predator transfer of enriched 15N-contents: basic laboratory data for predation studies using 15N as marker

As an alternative to methods currently used to study predation under field conditions, we propose to mark prey with (15)N, and to subsequently trace this label in the food chain. Preliminary laboratory work to develop this method is presented. The (15)N-content of polyphagous predators that have ingested (15)N-marked aphids was analysed with respect to: time after ingestion, the number of ingested (15)N-aphids, ingestion of additional non-marked prey, and predator size. Increased (15)N-contents were detected in solid feeders [Platynus dorsalis (Pontopiddan), Coleoptera: Carabidae], as well as in fluid feeders [Erigone atra (Blackwall), Araneae: Linyphiidae] up to 11 days after ingestion. The increased (15)N-levels were constant over time from a few days after (15)N-ingestion onwards, and correlated with the number of ingested (15)N-aphids. The ingestion of additional non-marked prey had no statistically significant influence on the predators'(15)N-contents. The (15)N-contents of carabid species with varying biomasses could be compared directly. Our results are compared with literature data of other methods (e.g., ELISA).