D3173: Determining tissue turnover rate and stable isotope fractionation rate of bronzed tiger beetle (Cicindela repanda) larvae through a diet switch experiment

Carbon and nitrogen stable isotopes hold information on an organism’s relationship within the food web and how energy flows within a consumer. An organism’s trophic level can be deduced by determining the δ15N value because 15N fractionates at a relatively constant amount between trophic levels, while δ13C undergoes lower levels of fractionation and thus is used to determine the primary producer of the food web. Tiger beetles (Coleoptera: Carabidae) are important bioindicators because they are easy to collect and rapidly respond to environmental changes. We used bronzed tiger beetles (Cicindela repanda) to determine the tissue turnover rate and stable isotope fractionation rate of tiger beetles by implementing a diet switch experiment. Sixty-two larvae were collected along the South Saskatchewan River in Saskatoon, Saskatchewan mid-summer. The larvae were placed into 532 ml cups filled 2/3 with native substrate and were allowed to form a burrow. Once habituated, they were watered and fed Trichoplusia ni caterpillars every second day. The larvae were kept in a growth chamber set to an 18:6 day:night cycle with an RH of 30% and a temperature of 24˚C during the day and 18˚C at night. Four larvae were sampled at select intervals. Additionally, four pupae, ten adults, T. ni caterpillars, and caterpillar diet were also sampled. All samples were then dried and crushed into a powder. 1.0 mg ± 0.2 mg animal tissue was placed into aluminum cups which were sent to the National Hydrology Research Centre for stable isotope analysis which is currently underway.