The chemical defense of leaf beetle larvae represents a complex system of intercellular transport processes and enzymatic conversions, which often begins already in the secondary metabolism of the plant and ends in the deterrence of a predator, or the inhibition of microbial pathogens. This functions are realized mainly through defensive secretions, which is produced in nine pairs of accessory defense glands in the larval back and is presented as droplets on dorsal papillae in the event of an attack. In earlier work, a highly selective transport system for the chemical precursor and the biosynthetic principles for the generation of the bioactive allomones has been identified. Since usage of plant secondary metabolites for defensive purposes is a quite distributed feature in arthropods, knowledge about the functionality of the system in these beetles, also helps understand other systems. The aim of the thesis was to use the recently generated transcriptome databases of selected species of the subtribe of Chrysomelina, to reveal the molecular base of transport and biosynthesis, which was mainly unknown so far. By establishing and using RNA interference on our model systems Phaedon cochleariae (Fabr.) and Chrysomela populi (L.), proteins from the fat body, the glandular membrane and secreted ones were targeted. By the essential integration of adequate controls for each target transcript and a corresponding analysis strategy, investigating the generated “loss-of-function” phenotypes, transcripts could be identified responsible for certain steps in the defense metabolism. Due to the ongoing sequencing of closely related species, a comparable approach could be done relatively quickly. With the knowledge of the molecular base of the altered defense biochemistry of other species, new insights into the evolution and speciation of the leaf beetles could be obtained.