[en] Studies on chemical ecology of host plant selection by herbivores were largely carried out to
explain the diversity of secondary plant chemicals and host specialisation of herbivores. The
glucosinolate – isothiocyanate system in Brassicaceae plants was considered as a plant
defence and was known to influence the feeding behaviour of phytophagous insects such as
the cabbage aphid, Brevicoryne brassicae. Purified myrosinases from the latter and from
white mustard, Sinapis alba, were used to hydrolyse two glucosinolate compounds.
Identification of the degradation products, mainly isothiocyanates, was performed by gas
chromatography – mass spectrometry. While sinigrin hydrolysis gave identical
isothiocyanates for insect and plant enzymes, B. brassicae myrosinase showed a particular
activity toward sinalbin. A lost of an hydroxy group was observed for the two latter substrates
related products when compared to the S. alba enzymatic specificity. Aphid and plant
myrosinases have different properties and specificities which can be discussed in relation to a
co-evolution approach.