The phenolic profiles of cabbage white butterfly ( Pieris brassicae L.; Lepidoptera: Pieridae) at different development stages (larvae, exuviae, and butterfly), its excrements, and its host plant Brassica rapa var. rapa L. were determined by high performance liquid chromatography- diode-array detector-mass spectrometry/mass spectrometry-electrospray ionization (HPLC-DAD-MS/MS-ESI). Twenty-five acylated and nonacylated flavonoid glycosides and ferulic and sinapic acids were identified in host plant, from which only 12 compounds were found in the excrements. In addition, the excrements showed the presence of sulfate flavonoids and other flavonoid glycosides that were not detected in the leaves. In the larvae kept without food for 12 h, only 3 compounds common to the plant material and 2 others, also present in the excrements, were characterized. The results indicate that deacylation, deglycosylation, and sulfating steps are involved in the metabolic process of P. brassicae and that its excrements may constitute a promising source of bioactive compounds, which could be used to take profit of this common pest of Brassica cultures.

For the first time, an insect-plant system, Pieris brassicae fed with Brassica rapa var. rapa, was tested for its biological capacity, namely, antioxidant (DPPH*, *NO, and O(2)*- radicals) and antimicrobial (bacteria and fungi) activities. Samples from the insect's life cycle (larvae, excrements, exuviae, and butterfly) were always found to be more efficient than the host plant. Also, P. brassicae materials, as well as its host plant, were screened for phenolics and organic acids. The host plant revealed higher amounts of both compounds. Two phenolic acids, ferulic and sinapic, as well as kaempferol 3-Osophoroside, were common to insect (larvae and excrements) and plant materials, with excrements being considerably richer. Detection of sulfated compounds in excrements, absent in host plant, revealed that metabolic processes in this species involved sulfation. Additionally, deacylation and deglycosilation were observed. All matrices presented the same organic acids qualitative profile, with the exception of excrements.