TROPHIC LEVELS AND ANOMALOUS DELTA-N-15 OF INSECTS ON RASPBERRY (RUBUS-IDAEUS L)

Unexpectedly elevated delta(15)N values (8 to 16 parts per thousand) were found in adult raspberry beetles (Byturus tomentosus), collected shortly after emergence from over-wintering sites. Elevated delta(15)N values (11 to 14 parts per thousand) were also found in over-wintered larvae, but young adults, collected shortly after metamorphosis in autumn, and larvae collected from raspberry drupelets and receptacles in summer, did not show such elevated delta(15)N. delta(15)N values of feeding larvae (similar to 2 parts per thousand) were close to those of their food plant, red raspberry (Rubus idaeus). The elevated delta(15)N values in overwintered larvae and adults of raspberry beetle are consistent with an hypothesis of extensive amino acid nitrogen recycling during prolonged fasting. Predatory seven-spot and two-spot ladybirds (Coccinella septempunctata and Adalia bipunctata), (delta(15)N similar to 7 parts per thousand) showed an expected trophic level increase of similar to 1 parts per thousand relative to their prey, the large raspberry aphid (Amphorophora idaei). The potential is assessed for using continuous flow isotope-ratio-mass-spectrometry (CF-IRMS) at natural abundance levels for studying invertebrate development and food webs.