Whether horseradish flea beetles deter predators depends on their food plant and their life stage

Horseradish flea beetles use glucosinolates from their host plants for their own defense. They have an enzyme which converts glucosinolates into toxic mustard oils. Researchers at the Max Planck Institute for Chemical Ecology in Jena, Germany, found that while glucosinolates are present in all life stages of the beetle, the enzyme required to convert these into toxic substances is not always active. Although larvae fend off attackers, pupae are predated because they lack enzyme activity.