Seven plants in the chitin treatment were supplied with approximately 15 mg of chitin from shrimp shells (95% acetylated,
Sigma Aldrich, St. Louis, USA) every week for 16-week-long feeding
period (in total 240 mg of chitin per plant for 16 weeks). We analysed
the nitrogen content in chitin and we found 64.8 mg N g1
DW. Thus each fed plant obtained a total of 15.6 mg of nitrogen
during the whole feeding period. Another seven plants were fed on
protein with approximately 6 mg of BSA (Sigma Aldrich, St. Louis,
USA) every week for the same feeding period (in total 96 mg BSA
per plant for 16 weeks). The analysed nitrogen content in BSA was
144.2 mg N g1 DW, thus each plant obtained in total 13.8 mg of
nitrogen during the whole feeding period. Both substances were
applied on two or three fully developed traps covered with sticky
tentacles during each feeding. Thus both groups of plants obtained
approximately the same amount of N in the form of chitin or BSA
(ca. 14e16 mg) to investigate the nutritional value of both substances
commonly found in insect prey. Seven plants served as
unfed control. After 16 weeks of feeding, the plants were allowed to
grow for another 6 weeks without any additional feeding before
they were harvested for analysis. This period was necessary for the
production of new leaves used in elemental and isotopic analyses
which were not contaminated with remaining BSA or chitin applied
on trap surface.