Some allelochemicals of Pteridium aquilinum and their involvement in resistance to Pieris brassicae

A number of polar and semi-polar compounds from bracken, Pteridium aquilinum L. Kühn, were screened for feeding deterrent activity to Pieris brassicae L. At natural concentrations, 2 out of 4 flavonoids tested were stimulatory and one was inhibitory; while 2 out of 4 benzoic, and 4 out of 5 cinnamic acid derivatives were inhibitory. Prunasin and its enzymatic hydrolysates had no effect on feeding. It was concluded that braken flavonoids and cyanogenic glycoside were unlikely to be involved in resistance of polar bracken extracts to P. brassicae, while benzoic and cinnamic acids and condensed tannins were probably involved. A number of other benzoic and cinnamic acid derivatives not occurring in bracken were screened, and distinct relationships between chemical structure and feeding deterrent activity to P. brassicae were demonstrated.