Trophic Levels and Anomalous δ15N of Insects on Raspberry (Rubus Idaeus L.)

Unexpectedly elevated δ 15 N values (8 to 16‰) were found in adult raspberry beetles (Byturus tomentosus), collected shortly after emergence from over-wintering sites. Elevated δ 15 N values (11 to 14‰) 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 δ 15 N. δ 15 N values of feeding larvae (∼ 2‰) were close to those of their food plant, red raspberry (Rubus idaeus). The elevated δ 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), (δ 15 N-∼7‰) showed an expected trophic level increase of ∼1‰ 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.