All samples were placed in tin capsules (5 x 9 mm, Costech Analytical Technologies, Valencia, CA, USA) and weighed to 180 ± 50 μg for muscle and 220 ± 50 μg for hemolymph. δ13C and δ15N were analyzed with elemental analyzer/continuous flow isotope ratio mass spectrometry at the Center for Stable Isotope Biogeochemistry at UC Berkeley using a CHNOS Elemental Analyzer (vario ISOTOPE cube, Elementar, Hanau, Germany) coupled with an IsoPrime100 Isotope Ratio Mass Spectrometer (Isoprime, Cheadle, UK). Isotope ratios are expressed using δ notation as:
where X is the element, h is the high mass number, R is the high mass-to-low mass isotope ratio, and Rstandard is Vienna Pee Dee belemnite (VPDB) for carbon and AIR for nitrogen. Units are parts per thousand (per mil, ‰). We used peach leaves (Standard Reference Material [SRM] No. 1547, n = 105, mean ± standard deviation: δ13C = -25.9 ± 0.1 ‰ and δ15N = 2.1 ± 0.1 ‰) and bovine liver (SRM No. 1577, n = 38, δ13C = -21.54 ± 0.1 ‰ and δ15N = 7.9 ± 0.1 ‰) as references to correct the stable isotope ratios for drift and linearity of the mass spectrometer.
where X is the element, h is the high mass number, R is the high mass-to-low mass isotope ratio, and Rstandard is Vienna Pee Dee belemnite (VPDB) for carbon and AIR for nitrogen. Units are parts per thousand (per mil, ‰). We used peach leaves (Standard Reference Material [SRM] No. 1547, n = 105, mean ± standard deviation: δ13C = -25.9 ± 0.1 ‰ and δ15N = 2.1 ± 0.1 ‰) and bovine liver (SRM No. 1577, n = 38, δ13C = -21.54 ± 0.1 ‰ and δ15N = 7.9 ± 0.1 ‰) as references to correct the stable isotope ratios for drift and linearity of the mass spectrometer.