Glucosinolates are plant defense compounds that deter herbivores. The general structure of glucosinolates includes sulfur, nitrogen, and a glucose sugar. The difference in the R-side chain gives each mustard oil its own particular flavor and character. In the presence of the enzyme myrosinase, the glucose portion is hydrolyzed leaving a reactive isothiocyanate (mustard oil). Under normal conditions, glucosinolates and myrosinase are stored in different compartments. However, when plant tissue is damaged (as in the case of an insect feeding on the leaves), the enzyme is released and reacts with glucosinolates to release isothiocyanate mustard oils into the tissue.
The isothiocyanates are relatively toxic have been shown to be biocidal. Depending on the dose, everything from insects, worms, fungus, bacteria, to cancer cells can be killed by various mustard oils. Of course, in low doses we humans can find them delicious; but to something small like an insect, ingesting a mouthful of isothiocyanates is probably unpleasant. This deters some insects from feeding on Brassicales.
To protect the nascent buds, we placed mesh tents over the young Cardamine to keep these insects out. Later on, we can control plant exposure to herbivores by selectively placing a set number of Scaptomyza larvae with the plants.