Аннотация:In laboratory experiment the dynamics of stable isotopes ratios (d13C and d15N) in the tissues of Pterostichus oblongopunctatus and Platynus assimilis were studied. Four different diets were used: bloodworms, seeds of Poa pratensis, mixed diet, without food. Every ten days five males and females of each species were dissected and the samples of muscles (prothorax), chitin (elytra), fat-body, excrements, and gonads were taken. The differences of isotopic composition
of gonads and muscles were observed in both species. These differences were significant on animal and mixed diet, but were not clear on seed diet and by fasting. The range of d15N value measured up to 7%o in muscles, and to 4%o in gonads. In muscles the content of both heavy isotopes increased distinctly, however its values were on 2-5%0 lower as compared to diet. In gonads of both sexes on animal and mixed diets the value of d15N was above than in food on 1- 2%o. The mean values of 813C and d15N in chitin were relatively stable in both species during whole experiment and not significantly differed from control. Thus we conclude that: (i) in ecological studies d13C and d15N values must be estimated in the separate tissues that prevent the distortion ofresults; (ii) the differences in content of stable isotopes in chitin would be used as a criterion in the studies of migrations of carabids; (iii) the individual variations of d15N value in different tissues are high and can exceed the limit of formal "trophic level" (see Post, 2002; Ikeda et al., 2010).
